Welcome Olrac to the GMAT Club forums. I think you made the right step to join our community here and eventually you'll start appreciate this forum and its members when you raise the bar of your desired score on the GMAT.
Cracking the GMAT by PR is a very decent GMAT book for beginers. The book intruduces you to the idea of the GMAT exam and its construction [different sections and timing] . The book also introduces you to many basic and intermediate concepts in math and verbal. I believe Cracking the GMAT by PR and Kaplan books are the best ones out there for beginers.
Now, after you're done with the book DO NOT take the GMAT. You'll need to buy the
Official Guide 11. It's made by the makers of the GMAT. it's not a learning tool with the same type of instructions as the Cracking gmat, it's more of an official practice source with 800 questions from previous GMAT exams, including answers and explanations.
Once you're done with the
OG 11 start doing the 2 full-length practice tests "The GMATPrep" you can obtain from
https://www.mba.com .
If you're aiming at 600-650 I bet you'll get enough prepration. If you're looking for above 700 then you may need Kaplan 800 and some other stuff.
The Main Key: one of the best preparation tools for the GMAT is this
forum. participate and be an active member, post questions that you don't understand, answer questions posted by others, and read ALL the stickys in the forms and you'll see a HUGE difference in your perception and idea of the GMAT.