creating music

https://musescore.org/en/handbook/measure-operations#append ?

Enter notes until you need more measures. While you're entering notes, the measures will change sizes to accommodate the notes. When there are too many measures on a staff, a new one will be made, it works like word wrap in a word processor. Press shift+alt+B to add more measures. When the measures fill the page, a new page will be created automatically.

These are the basics. There are way too many other options. You would do yourself a favor to familiarize yourself with the handbook.