GMAT Math Section
GMAT Problem Solving
Roughy half of the GMAT Quantitative section is GMAT Problem solving, a familiar five option multiple choice format.
GMAT Data Sufficiency
The balance of the math is Data Sufficiency, a testing format unique to the GMAT quantitative section. For GMAT Data Sufficiency you don't provide an answer but need to judge whether with the given information you can provide an answer, whether the given information is sufficiency (get it, Data Sufficiency).
How to Study for GMAT Math?
Normally GMAT Quant take less effort and time to study for than GMAT verbal. That's not say that you can slag off. It still takes effort. But if you struggle with verbal that's most certainly the thing to attack first especially the reading comprehension and critical reasoning as reading skills take time to develop. It's also the case that as you improve reading and reasoning skills that should improve your quant well. Not only is there plenty of reading in GMAT word problems but in general this is a reasoning exam. So even on the quantitative section it's not the math that's challenging it's the reasoning.
-Stick to official GMAT quant questions and tests especially as you get nearer to your exam
-If you are going to use third party quantitative questions then use them more to build up your basics than to evaluate progress or apply skills. The more you get into application and practice tests shift over to Official GMAT quant questions to make sure you're 100% on point in terms of content and flavor.
-Start your preparation more targeted and then shift to more mixed sets and practice tests. Don't blast practice tests in the beginning of your preparation except for one diagnostic at the beginning.