There are two Official GRE guides that I recommend students to use for preparing for the quantitative reasoning section of the GRE. The main official GRE guide is called the Official Guide to the GRE General Test 3rd Edition. This guide should be your starting point. The link below will take you to my video explanations to all of the questions in this guide.
The second guide is called the Official GRE Quantitative Reasoning Guide. You can use this guide to supplement your practice work. The link below will take you to my video explanations to this guide.