Don't edit text on a master page. They are for repeating elements only, and you may actually forget to include such a page in your actual document (in which case it will not appear in your output), or use it more than once (and you end up with two same pages).
First "apply" that master to a blank new page so all of its elements appear, then use Cmd (or Ctrl)+Shift plus a mouse double-click on the element to make a local copy on your actual page, and edit at will. InDesign will remember you 'detached' the object from a master, and the original will disappear from that one page.
If you are serious about working with InDesign, consider taking an online course (Lynda) or buy a good beginner's tutorial book (anything from Sandee Cohen for your version). (For one, they will both remind you of the proper capitalization of the trademarked name "InDesign" 😉)