So, theres 2 different types of overclocks? What does each do? Sorry, I'm very new to this.
Yep. You can overclock the CPU, the GPU, or both at the same time, if you want (I do).
Overclocking the CPU helps overall system performance and
gaming, while overclocking the GPU only helps in gaming.
Both together can help gaming performance quite a bit, although I'll say that I don't think you, specifically, even need to overclock anything. You should be golden with what you have.
The 3550 is more than powerful enough to keep up with the 7870 (a 3550 can keep up with any
GPU) and the 7870 should be fast enough at its stock speed to play most any game you want with good FPS.