The curves adjustment is a powerful tool that can do a lot - even replacing multiple adjustment layers (ex. Brightness/Contrast, Color Balance, Photo Filter, etc.). But it's not intuitive at all. Before you can even begin using the curves adjustment, you first have to spend time learning it.
But it doesn't have to be this way. The curves adjustment can be designed so that even if it's your first time using it, you'll be able to get a general feeling of how it works without spending so much time learning how to use it first.
In this video, you'll see 5 improves that can be made to the curves adjustment and in the process, you'll also better understand how the tone curves work.