If you’re a starting C language and want to learn how to develop games using SDL2, then I would highly recommend this tutorial series. They are a great introduction into programming in C and using the many features of SDL2. They hold your hand, but also force you to look at the source code to learn what’s going on under the hood. If you’re like me and re-write what the author writes it will help solidify a lot of the concepts. You can even mod the tutorials for extra practice.
Best $5 (or more) you can spend with regard to learning SDL2.