What exactly should be in this type of contract? Well, firstly you need to be aware of any laws in your country regarding employing people. It is likely these laws will override your agreement so it makes sense to line them up so they match. Then you need to put the basics in there. This might include hours of work, what their role is and how much they are going to be paid. After this, it is a matter of adding some other clauses to protect both you and the employee. This could be to do with dismissal and other situations that might arise.
When you find yourself considering going into business together you might want to consider how you are going to protect yourself in the event of a disagreement. If you are not planning to form a partnership you can always use a joint venture template to draw up an agreement that will protect all those involved in the venture. Considered a legally binding contract, you will find that when properly filled out this document will leave little for any errors or the type of misunderstandings that can cause what is otherwise a good, solid working partnership.