Help with musescore 4

By "bar" do you mean palette, the panel on the left side of the screen that contains elements you can add to the score. If so, see https://musescore.org/en/handbook/4/palettes#Resetting_a_palette

In fact, if you are new to Musescore, I suggest you read through the whole manual to at least find out what Musescore calls things, and the sirt of things it can do (and can't do).

And if you get stuck this is definitely the place to come. There are plenty of other users who have already had the problems you might encounter and are happy to share their experience