Hi there,

It is advisable to apply for colleges before CAT exam. You must apply for IIMs while filling application form of CAT. For other colleges also you must apply before results are out. As usually most colleges have deadline of register before results are out. So,you should visit different website of colleges and apply for them before deadline. You can apply for some college according to your interest and that you find decent enough for study. Colleges does not accept application after deadline.

Hope it helps you

Good luck!