Definition
To gain an easy victory.
To dominate, treat (someone) as inferior.
Origins
In the sense of gaining an easy victory, refers to a horse going over a racecourse at a walk when there is no other entry.
How People Actually Use It
walk over someone to treat someone badly and to make them do what you want without respect for their feelings walk all over someone
"I'm not about to let them walk all over me. They walk over close to the oil stove and stood there warning their hands."
Source: Urban Dictionary