QoS is one of the most advanced network topics there is. You must have a firm understanding of basic subnets and how networks session really work to even think to look at QoS. It is not possible to provide a simple explanation
The simple answer is your router does not have the features you need to even attempt to accomplish what you want. Even though it appears to have lots of options most do nothing. The critical feature it is missing is the ability to limit traffic to a fixed value.