I don't know what undergraduate program you have gone through, but this is definitely second-year or third-year course material for most physics degrees in universities. Maybe if you've already taken lots of AP classes in high school then you might be able to skip some stuff, but we're talking about the standard curriculum here.

Normally, you first study the distinction between vectors (which can be expanded to tensors) and scalars in second-year Analytical Mechanics class. You also get a taste of tensors toward the later material in Electromagnetism (which is also probably second-year). And you finally arrive at a rigorous definition of tensors when you take Mathematical Physics (second-year or third-year depending on your skills).