How to solve this imperfect square root?

need help solving for imperfect square roots for my homework, and I have a test for it soon. I have to simplify the sq. root of 378. and i need to simplify the sq. root of 72. If you could, can you explain how to do this so i know how to do it from now on. Basically I need a step by step process on how to simplify the sq. root of 378.