You need a database, a host or setup apache on your local machine, then you need to get an editor, like notepad++ if your on a pc. Then you need to create some tables and stuff in the database, then like connect to it in the code, and do stuff like, add-list, edit-list, delete-list, register, login, logout etc.

An auction site isn't exactly simple to do, you need to have to good security on it.