"Mom, why are you wearing my shoes?"
Translation:Mamá, ¿por qué usas mis zapatos?
Tus is a possessive plural for your: tus zapatos - your shoes, the possessive here is mis - my shoes.
What you're translating here is essentially 'you wearing', so it's the conjugated form of usar - to use:
Usted usa or tú usas.
...usas mis zapatos - you are wearing my shoes, or you wear my shoes.