How to prepare for GMAT Quant

Hello All,

Its being around 3 weeks since I have started preparing for GMAT. I started with MGMAT Guides for the Quant preparation and I am still not feeling confident on Geometry, Combinations, Probabilty and Number Theory. From where I should study all these topics? Can I study these topics from Arun Sharma's Quantitative Aptitude for CAT? Also, I am very confused about how should I prepare for the overall GMAT quant?

Please advice Bunuelbb

Thanks in advance