What book are you using? It does not look like a very clear textbook. Look for a college-level book if you are that age -- there are several good ones:
Nachalo
Golosa
V puti.
I think the чей stuff is too complicated for someone at your level. Get a good textbook and read it through in sequence, don't jump around. These three series also come with a workbook, and, I think, DVDs.