"I suppose I will make a sandwich"
"She will be alright, I suppose"
"But we were supposed to go to the mall"
"You were supposed to finish that assignment by Friday"
Chances are, if you are saying "suppose to" -- you are WRONG.
"Can I use your toothpaste?" (this has a 'hard' s.. like a z)
"That restroom is not for public use" (this has a 'soft' s)
"I used to go to that elementary school"
"We used bleach on our stained sheets"
"Used" happened in the PAST.
Chances are, if you are saying "use to" as a way to talk about something you are no longer doing-- you are WRONG.