How do you make more than one page in the studio?

https://musescore.org/en/handbook/measure-operations#append
or https://musescore.org/en/handbook/breaks-and-spacers
but I may not have figured out what you meant.

Studio does not make sense in English music, perhaps you mean the score? If so, as you enter notes, the measures will automatically become wider and move measures that no longer fit on the current line down to the next. When there are too many lines on the page, a new page is made automatically to allow for the extra lines. If you want the layout breaks to happen earlier than MuseScore puts them in automatically, you can use system breaks and page breaks from the breaks and spacers palette. Select the last measure you want on a page or line and double click the proper break to apply it as explained in Shoichi's link.