How to Change Note Lengths Easily?

How do you alter the lengths of the notes? This is the second or third time I've installed MuseScore and got frustrated with it and I'm on the verge of giving up again. I really want to be able to get along with this program because my mind thinks in terms of traditional notation and it looks professional and it's easier to read than other formats (piano roll, tracker, etc.). But at the moment this program's driving me crazy and I getting bogged down trying to understand the programming logic and this is preventing me from being able to be creative. And this is particularly disappointing after watching Tantacrul's videos and hearing so many good things about how all the other bad UI things have been fixed, so I really didn't expect to find basic tasks so difficult.

Here's an example: I had a bar in 4/4 consisting of a half note rest followed by two quarter notes. And I wanted to change it to a quarter note rest and two dotted quarter notes. So I selected both quarter notes together using the shift key and I clicked on the dotted note button. And suddenly I found myself with a tie and an eighth note and everything was all messed up and the next bar got altered as well, which is totally not what I wanted! And I clicked on various buttons and selected things and hit the delete key to try delete the crap (we've got an 1/8 note rest making an appearance now too) and fix the problem and it just got worse and worse! I did eventually achieve what I wanted via some long sequence of steps but I've no idea how I did it nor why the program behaved as it did nor how to make the program behave itself properly or how to edit anything else with risking damaging other notes in the same bar or the next one.

(1) I get that I can't have a half note rest plus two dotted quarter notes in a single bar of 4/4 because 1/2 + 3/8 + 3/8 > 1. But I hadn't finished inputting my request before the program started performing automated actions! I'm inputting using a laptop trackpad and I don't see how I can simultaneously have the quarter notes selected and click to make them longer and at the same time have the rest selected and perform a different action on it to make it shorter. Selecting two different things and performing two different actions on them just isn't something a trackpad can do. I'd need to have a multitouch touchscreen or something in order to be able to press two buttons at once! I used to work with databases and my analogy to my current problem is that MuseScore is trying to enforce the database integrity constraints before I said yes to "committing" my transaction.

(2) Having the two notes selected and clicking on the dotted note button seemed to make the first one into a dotted quarter note and the second one an eighth note. I get that a 3:1 ratio is a common use case but that's not what I wanted in this case. It's also not what asked the program to do. That's not how selections and toolbar buttons usually work. Selecting two words in MS Word and clicking the "bold" button doesn't result in some kind of "AI" kicking in and going, "Oh, I think your document would look so much nicer with one word in bold and the other in italic!" The icon doesn't look like two notes, one long and one short. It looks like a single dotted note. So that's what I expected it to draw: dotted notes (only). The tooltip also describes it as "Augmentation dot. Toggle duration dot." It doesn't say "Toggle dotted rhythm."

(3) Pressing the delete key doesn't do a proper delete. As in "Create empty space" or "Remove this object from the document", like it does in every other app ever. But in MuseScore it just creates more and more rests. What I'm desperate for is to create some empty space, some breathing space so that I can compose without the program inserting all those ties because the bar becomes overfull.

(4) At some point I eventually got the right symbols to appear but in the wrong order. So I'm dragging this rest trying to move it from the end of the bar to the beginning of the bar. But the program won't let me drag a note or a rest back past a previous note.

(5) This operation is so easy in the other composition programs I've used. Those programs use a piano roll representation and it's easy in those programs. I would just drag the two quarter notes backward into the empty space before them (equivalent to splitting the rest into two smaller rests and then having the notes swap places with one of them) and then I'd drag from a different part of second the note's rectangle to simultaneously extend the length of the two notes and remove empty space next to them (i.e. remove the second rest).

(6) I keep trying to deselect things and it randomly moves the entire page around. Eh? I didn't use a two fingered scroll gesture so why's it doing that?

How do I make make MuseScore behave itself and act sensibly? How do I stop it from checking the integrity of my score performing these automated "fix up" actions until I've finished making all of the changes to the bar that I want to? I noticed that if I long click on the pencil icon then a variety of different drawing modes are available. Will any of the other modes let me edit my score in the intuitive way that I want to do, so that I can experiment freely with things?

Thanks.