The three primary search options are Author, Title and Subject. These will suffice for the majority of searches you may attempt. Choose database allows you to choose a particular library database to search. Not all libraries are available through here. If you want you review the searches you have made thus far, select Search Review to see what you have searched for this session.
Intermediate mode has no real effect on searching.
Default Sort will give you options on how things will be sorted during your session. It's best to just leave it alone. If you want to see what books you currently have checked out or what fines are pending against you for late returns, select Borrower Info. It will prompt you for an ID and a PIN number. The ID is the 14 number bar code on your library card.