Generally with a rent or lease-to-own home you agree to pay $XX amount each month in rent, with a specified portion of that monthly payment set aside toward the purchase of the house. You also agree to the final sale price and the term, or length of time, you will be renting. When you reach the appointed date, you make a lump or balloon payment to the seller, and take possession of the home. The money set aside from your monthly rent payment is used as a down payment on the house, and deducted from the ultimate sale price. How you actually pay is up to your circumstances- most buyers I have worked with in this situation get a traditional loan.
However, what Ron has experienced in California holds true for the parts of MA and NH that I work in- lease to own homes are few and far between. They offer a much greater risk to the seller and the buyer, risk to the home itself, and plenty of work for little compensation for an agent.