How did the Dursley's treat Harry Potter?

Answer 1

The Dursleys severely abused Harry, mainly emotionally, by never allowing him to do anything, originally forcing him to sleep under the stairs, spoiling Dudley while not even bothering to give Harry the bare minimum of respect, talking badly about Harry's parents, and never really making Harry feel like part of their family.

Answer 2

They treated him very unfairly, leaving him with a cupboard for a bedroom and often locking him in it whenever he displayed accidental signs of magic. He was always second best to their son and Harry only ever received second hand clothes and smaller meals.