As some of the replys mention above, dont worry too much at this stage. as long as you are prepared to put the study in, most of the ATPL theory books provide detailed explanations from the view of a zero hour student. Some are far more detailed than others (the Oxford books i used were very detailed), i have heard the Bristol books tell you what you need to know. Dont rush, if you need longer on a certain subject, then do so, and learn as much as you can. There is a database to help you with the exams available, but you cant fly commercially on the back of a database.its many many hours of study and sacrafice.
There are also CBT disks available produced by Oxford if you need to brush up on Maths including trig, Nav and physics ect.Use all the resources at your disposal to help you.
Good Luck!