you use the spell books to learn your skills.
Not every class can learn every skill, and you also need to be the correct lvl to be able to learn it.
If you click in the library section to the left on this page you can choose "skills" and read up on when and what skills your character can learn.
Also, at your level, and being new to the game, you might be best off to buy the books as you need them. In otherwords, you get to a new level, say maybe 7 (it varies with the class), you go to an NPC and ask for training, you will see a list of skills you can learn. Some of the skills, but not all, will require a spellboook, and you will find out as you try to learn the skills.