How to add multiple tracks to MuseScore?

Disclaimer: I have no idea at all what the limitations as a blind user are.

You should be able to go into the Edit menu to find an entry called "Instruments" (or use the default shortcut key 'I'). This opens up a window which (to the visible) has a list of possible instruments on the left side, with an input field allowing you to search through/filter that list, and then a middle section containing Add/Remove buttons. Activating the add button will place the selected instrument on the bottom of the list at the righthand side of the dialog, which contains a list of the instruments available in your score.

Hopefully this description gets you something usable :)

If you press the letter I it will bring up the instruments dialog. Not knowing you audio feed back and how well it works with dialog boxes, I'm not sure how to tell you to find a specific instrument. I experimented with the instruments dialog box, and pressing keys did not seem to have any effect. This seems to be a large short coming for a user who is totally blind. If you had limited eyesight and the ability to use the mouse, I could help you get started. Perhaps someone knows something I am missing.

As mentioned, pressing the menu Edit / Instruments or pressing the shortcut "I" will bring up the dialog that allows you to add instruments. The dialog is reasonably keyboard-accessible, although it is a little awkward.

In general, we did make an effort to make as much of the MuseScore keyboard-accessible (and screenreader-friendly) as we could for the 2.0 release. but there is much work left to do. It's still the case that some parts of the interface are not keyboard-accessible - the palettes most importantly. So unfortunately there are many markings you won't be able to add to your score. There is an effort underway right now to address this for a future release.

Meanwhile, if you haven't already, check out https://musescore.org/en/handbook/accessibility

I was going to put in a specific feature request to allow for access to the Instruments Dialog. I played around with my keyboard to see if it had any effect at all. For those who can see, when an item is selected using the tab button it is difficult to tell what is selected. Here is what I discovered about keyboard accessibility.

When the Instruments Dialog is opened the first time, the instrument group (such as common instruments, orchestral instruments, jazz instruments and so forth) will be selected. You can then tab down to the instrument list which is divided into instrument families (such as Woodwind, brass, pitched percussion and so forth). I will explain navigating the instrument list later. The next tab position is the search box that allows you to type part (or all) of an instrument name to limit the instrument list to those that contain the search words. Pressing Tab again will move to the clear button which will reset the search box to nothing. Pressing tab again will to any of six buttons that allow you to take actions with a selected instrument. If an instrument is selected from the instrument list then Tab will move to the Add button, which will add that instrument to the bottom of the list of current instruments which will I'll explain shortly. Pressing Tab again will move to the remove button, which removes the selected instrument from the current instruments list from the score. If a staff is selected, the staff will be removed. Pressing the Tab again will move to an arrow button. If the instrument in the current instruments list is not the first one, the up arrow is selected. This will move an instrument up in the score. The next Tab location is the down arrow, unless the instrument selected in the current instruments is the last instrument in the list. This allows you to move the instrument up in the score. The next tab location is add staff. It will only stop here if a staff is selected in the current instruments list. This is for adding a second staff to an instrument such as a piano or organ. The next tab location is add linked staff. This is normally used to add a tablature staff to a plucked instrument such as guitar or lute, but not violins or harps since these do not use tablature staves. The next Tab location is the current instruments list. The last selected instrument in this list will be selected. I will explain navigating this list shortly. The next Tab location is the Load... button, which allows you to load an instrument list. The next Tab location is the Save... button, which allows you to save an instrument list. The next Tab location is the OK button, which accepts any changes you made to the instruments list. The next tab location is the cancel button, which closes the instruments dialog and none of the changes you made will be reflected in the score. Note: pressing I at any time the instruments dialog is open will be the same as selecting cancel. Pressing tab again moves into the current instruments list and selects the staff type of the first instrument that has the staves visible. Continuing to press tab will go through each of the staves in the current instruments list. Pressing Tab when the last staff is selected will start again with the Instrument group.

The next time you open the instruments dialog, the last item you had selected when you closed the dialog in any way, will be selected. All other setting in the dialog will be the sames as when you closed it with the exception of any changes you made, such as adding and instrument or delete a staff.

Now for information about the Instruments list. The fist time you open the dialog, the instruments group will be Common Instruments. The up and down arrows will cycle through the different instrument groups. In the Instruments list, all instrument families will be collapsed. The first time you press tab to get to the instruments list, a > next to the first instrument family will be selected. To expand an instrument family, press the right arrow. To collapse an instrument family, press the left arrow. To move up and down the visible list, press the up and down arrows. The instrument family names are never selected, only the > next to it. The instrument groups determine which instrument families are listed and which instruments are listed under any instrument family. Pressing Enter with an instrument selected will add it to the current instruments list as the last instrument in the list. It will also become the selected instrument in the current instruments list.

In the current instruments list, the default is for the staves under each instrument to be expanded. For example, the default behavior is for the flute to have one staff listed and the piano to have two staves. To collapse a list of staves under an instrument press the left arrow while the instrument is selected. To expand the list of instruments press the right arrow while the instrument is selected. While the staff is selected, pressing the left arrow will select the staff's instrument while pressing the right arrow will scroll the view to the right so the type of staff is completely visible. If you press a letter, the first instrument in the list that starts with that letter will be selected. If you have an Oboe somewhere on the list, then an organ later in the list, the Oboe will always be selected when you press O. There is an exception to pressing a letter, pressing I any time you are in the instruments dialog will close the dialog and no changes will be made to the score. There is one item that has no apparent way to access, this is the visible check box for an instrument. This is for the current instrument to be visible in the score or not.

When you press tab after the cancel button, you move to a list that tell what kind of staff is assigned to that staff. This can be something such as standard, which is the only option for pitched instruments that do not use tablatures. If the instrument uses tablatures the list will include standard and a variety of different tablature staves. If the instrument is unpitched percussion, such as a bass drum, cymbal or drumset, the list will only include several percussion staves. To cycle through any of these lists of staves, press the up and down arrows, pressing tab accepts the staff and moves to the next visible staff. To be clear, if the instrument is collapsed, the staves will not be visible, tab will not move to that instruments staves and you will not be able to change the staff.

One final note, pressing Shift and Tab will move in the opposite direction as pressing Tab. This is as expected in most applications.