Everyone
Use everyone as a pronoun to mean all the people in a group.
Examples:
Do you think everyone will want to come to the party?
She wants everyone to leave comments on her blog.
Every one
Use every one as a noun to indicate each person.
Examples:
Every one of the students has a question about the grammar.
My boss told every one of the employees himself.
Do you understand the rules? Test your knowledge with this Everyone vs Every one quiz.