MSHybrid mode will Swap Between the IGPU in the CPU and Dedicated GPU depending on what its being asked to do that is where the light on the power button goes from White (IGPU) to Red/Orange (Dedicated GPU) and if it detects a heavy load will use the Dedicated GPU and if its a light one it will use the IGPU in the CPU to save power
Discrete Graphics Mode will lock the System on the Dedicated GPU only so its not ever using the IGPU this will use more power as the Dedicated GPU is alot more of a load on the Power Draw