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Is making mounds for potatoes nessicary? Someone told me this then grabbed my hoe from me and made mounds on some of my pototoe plants.

Mounding or earthing up potatoes is not necessary but if you don't you will get fewer potatoes and some will be exposed to the light, turn green and become inedible (poisonous).
An alternative to earthing up is to cut slits in a sheet of black polythene and allow the tops to grow through these.
In my experience earthing up is to be prefered

Yes, it is necessary. As pd said, if you don't, you get fewer pots and they are exposed to the light. The bigger the mound you build around it, the better