This one was helpful - Writing CAML Queries For Retrieving List Items from a SharePoint List and is fairly comprehensive.
Have a look at this tutorial. Hope this will help you in learning the CAML query basics. CAML Query tutorial for SharePoint
On MSDN you find a nice intro here: http://msdn.microsoft.com/en-us/library/ms426449.aspx
You can also use the U2U CAML Builder.