There's a classic standard most students (and professors) use when determining how much time to allocate for studying in college: For each hour you spend in class, you should spend 2-3 hours outside of class studying.
Of course, that "outside of class" studying can take on different forms. You might be doing the traditional, sitting-with-a-book in your room studying; you might be spending time researching in the library or online; you might be in a language lab; you might be in a science lab; you might be meeting with other students with whom you are doing a group project. And, of course, some classes require a lot more time while others require a little less.
Knowing how much time to spend studying in college is important because 1) you'll be able to gauge if you're spending enough time on your academics, 2) you'll be better able to manage your time well, and 3) you'll do better in your classes if you know how much time it takes an average student to adequately understand, learn, and engage with the course material.