[eluser]Sayian[/eluser]
Database is the easiest part of application design (if done right).
Checkout the mysql website for select, insert, update, delete ... once you learn the basic syntax, CI makes it stupid easy to write sql by using activerecord ... and its enabled by default.
The reason I would advise learning syntax from the mysql site first is that without a basic foundation the active record class might not make much sense if you don't even know what your goal for the query is.