CAT is a Management entrance exam which is conducted by IIMs. If you manage to get a percentile above 60 then you can get a decent college that will offer you a decent placement. 

You can definitely join coaching classes as that will help you with what you should study for the exam and at the same time they'll provide you test series that will help you to manage your time. But do join only the reputed Institutes like TIME, Career launcher, IMS or others.Apart from that you can get some books to study yourself. 

All the very best