hi i noticed i have a mushroom brown in color growing in my peace lily, so i got a bright light and looked closer and noticed little white bugs i think there spider mites and there are quite a few. how do i get rid of them and why the mushroom.

The mushrooms you can either leave them in or take them out, they won't hurt your plant.The spores can come from unsterilized soil.
If the bugs your seeing look like tiny little spiders with probably some fine webbing around the leaves on the plant, not in the soil, spray the plant down thoroughly with some soapy water until the plant is dripping wet, get every inch of the plant, including under the leaves using a spray bottle.

Do this every 5 days or so for three weeks, then keep an eye out, you want to get everyone of them or they can come back.

Keep the plant away from others so they don't get infested. I would cover the soil with some kind of plastic bag before spraying.The soapy water should be about the same strength/mix as you would use for doing dishes.