Parts is a MuseScore feature to aid extracting staffs to generate different versions of the same score.
A Part is an independent viewing profile that contains layout and formatting style configuration, Mixer settings and chord playback settings only. Most of the musical score data (except for certain items like image attached to first staff) is shared among Parts. Modification such as changing a note when viewing one Part will reflect on the same places if the item exists on other Parts.
Tempo markings are always shown on all Parts. Text and Line object's visibility depends on its object type, for example a System text added on any one staff is visible on all Parts, even if it is not included in that Part.
To manage Parts, open the Parts window by selecting File → Parts…, Parts are shown in Select Part pane.
New score file created contains no Parts by default. Full Score is shown, there are no sub-tabs under the score file tab:
score adapted from https://musescore.com/user/9928481/scores/5706424
When a score contains at least one Part, the Full Score and Part(s) are shown as tabs under the score file tab, click on any one tab to view it. Either the Full Score or any one of the Parts can be viewed at a given time:
Use Include or exclude Voices in a Part for the last two.
To add new instruments, see Change instrument setup instead.
A Part can be manually named, and include instrument(s) or their Voice(s).
To batch create separate Parts for each instrument:
Parts are only editable during creation - A bug in Musescore 3.6.2 prevents user from editing existing Parts. You may need to delete it and edit it during recreation.
Change Part name in Part title:, it is displayed at the tab heading. It is also used as filename suffix when exporting. You may want to rename Parts to prevent confusion if you have already changed the long or short name to something other than instrument name.
To add an instrument to an existing Part:
To remove instruments from an existing Part:
This feature is not working in Musescore 3.6.2 due to a bug, use Include or exclude Voices instead.
This feature only works if all notes need to be strictly written in separate Musescore Voice respectively. To extract, for example, "Flute 1 & 2 in the same staff" into two Parts, notes need to be strictly written in Musescore Voice 1 and Voice 2 respectively, even in passages where they share content, you might need to create duplicate Voice 1 unison and assign it to Voice 2. Flute 1 and Flute 2 notes should not be merged into one chord in one Voice at all.
piano left hand separation like shown above does not work
assign piano left hand notes to Voice 2 as shown above, working result is shown below
The same result can also be achieved without fiddling with note Voices assignment, because piano left hand is on the Bass staff.
When you delete Parts, most of the musical score data are intact, because Part contains layout and formatting style configuration and its playback options only
Instruments not included in the currently opened Part does not create playback by default, to change this behavior toggle Mixer Play Part Only option. This option is not modifiable when the "Full Score" is currently opened, as shown below. It is only modifiable when a "Part" is currently opened, for example, click either "Send to Chris" or "Print one for Jimmy" to open that Part.
To export Part(s):
Score file name will be used as prefix for Parts, generating files with the names "<Score file name>" + "-" + "<Part name>.<extension>". When exporting as PDF, an additional file named "<Score file name>" + "-Score_And_Parts.pdf" is generated.
To print a Part:
Parts are embedded into a score file, and saved along with the score file. No other action is required.
To save a Part as an separate file: