A desperate newbie

For days now I am trying to find out the following:

I bought a template and this template has 5 “menu”-buttons (About Us, Products, Contact US etc.)
After clicking on a button a window comes up with some text and a “read more”-button. When I click this button another window pops up with extra text.
Now I can change this text but…then this text is everywhere the same wherever you click the “read more”-button, also on the “other pages” like Contact US or Products.

How can I make the text & pictures for that specific “read more” button?

Please help, this is making me crazy!