There are two sections on overclock settings. One is for AMD GPUs and other one is for NVIDIA GPUs.
Overclocking works different for both so they both have different optimum values. You are going to have to find them by trying.
Everything you see in the name of core is about electricity, and memory is about hashrate.
We suggest that you give between 1100/1250 to core clock, and between 2000/2150 to memory clock in AMD GPUs.If you want to undervolt your AMD GPUs you have to select undervolting, by the time you select it, it will turn “YES, apply to all core states” then you are going to have to set the undervolting values of core clock, core state and core voltage. When you do, the important thing is to keep in mind that you have to sacrifice some of the hashrate of your GPU in order to undervolt it.
We suggest that you give between -250/+250 to core clock, and between 1000/2000 to memory clock in NVIDIA GPUs. Power limit is for undervolting in NVIDIA GPUs. It will limit the GPUs electricity consumption so you are going to have find the optimum hashrate for that power limit. It is not possible to get high hashrate and undervolt your GPU at the same time.