Why don't my users have access to the full range of editing functions.

Some of my students don't have the link option so they can't make their own pages within our class wiki. I may have invited them into the wiki using the wrong category. Also, som of them are prompted to give secret code before they can edit a page. What I'd like for them is to have the simplest access and I want them to be able to write their own pages and comment or write pages with others in the group.

What did I do wrong? What can I do to fix it.