CPU Vcore = core voltage. Your bread and butter setting for getting a stable OC via multiplier. Sandy/Ivy can run up to ~1.45v safely, however with Ivy you're unlikely to reach that voltage due to thermal limits without delidding the CPU.
CPU Vtt = CPU IMC setting. You will not need to change this unless you're trying to run something like 2133MHz RAM, and even then it probably won't need to be changed. Some of the older Z77 boards simply can't handle DDR3 at speeds higher than 2133MHz. If your RAM kit is on the QVL for the board just enable XMP and leave this setting alone.
IMC = Integrated Memory Controller voltage, see note above.
CPU PLL = voltage supplied to the Phase Locked Loop section of the CPU. For Ivy generally people recommend to run it at stock (1.8v) or actually lower it to the 1.5-1.7v range. I always left it at 1.8v, or raised it for some extreme OC cases. Maximum safe value is under 1.98-2.0v (there is no feasible reason to have it this high).
Dynamic GFX = voltage supplied to the iGPU of the CPU. Just leave it where it is.