Not all contracts have to be written in order to be enforceable, but some do.  Real estate contracts and any contract that cannot be performed within one year (like a lease of more than a year) must have written contracts.

Real estate agents are allowed to do a lease up to a year using pre-made legal forms.  These forms have been prepared by attorneys, and the real estate agent uses the check boxes to tailor the agreement.  Also, a lease of a year or less does not need witnesses to be enforceable.

When in doubt, seek competent legal counsel 

Attorneys do not have to be expensive and they do not have to be obnoxious.  Furthermore, an attorney can be the difference between an enforceable lease, and a useless piece of paper.