Help!

The word "everyone" refers to all the people in that place, the group: "Everyone enjoyed the party."

"Every one" is a modifying phrase which means the same thing as "each one", that is, each person individually -- "Every one of us enjoyed the party" You could also say "Each one of us enjoyed the party."

The same kind of distinction applies to every day/everyday, and any one/anyone. I'd be happy to try to clarify more if you like.