To make different pages come up in the main frame when you click on buttons or words that are links in another frame, first create the pages you want to come up there. Next, open the frameset. Click in the frame where links will appear, highlight whatever element (image or text) will the link, and then type in the link blank in the properties box:
Next to the link blank is the Target box. If you have opened the whole frameset -- not just the one frame containing links, but the whole thing -- options will appear in the target box called "mainframe," "topframe," "leftframe," "rightframe" (depending on the kind of frames you originally selected). Indicate the frame in which you want the linked material to appear.
Remember, if you create back buttons, as I have here, that you will want to link to the main frame of the frameset and then choose a target of self, or you will want to link to the whole frameset, choosing a target of top.
"_self" means that whatever is linked will replace whatever frame you are currently looking at.
"_top" means that whatever is linked will replace the whole window, not just the frame in which you are currently working.