"Spend time” is used to talk about the time you do an activity.
"Pass the time" means doing something to make the time pass faster while you are waiting for something else.
"I'm spending time at my mother's house."
"I spend my time reading books."
"I'm spending two weeks in London."
“I look at the magazines to pass the time while waiting for my appointment at the dentist’s office.”
"I trying to pass the time by reading a book"
"I pass the time by eating, sleeping and reading."