They are not as simple as the previous answers imply, they are very complicated when it comes time to exercise the purchase option so research the subject in depth before jumping in. They are probably not what you expect. Be careful putting up any large sum on a rent-to-own, most buyers and sellers are under the impression whatever deal they put together will be accepted by any lender when it comes time to actually purchase a home, not true. The mortgage underwriting guidelines are very specific and an underwriter may not agree with the terms on your original lease option. You may think all or part of the rent paid goes to down payment, not necessarily how it works when it comes time to close the deal.
As for rent to own, research the subject in depth before jumping in. It is probably not what you expect. In this type of transaction the underlying assumption is the seller will be able to perform in addition to the tenant/buyer. That is a very big what if, sellers are not subject to the same federal regulation as banks, do you really know the seller well enough to give them your hard earned money? I have discussed this in the blog entry linked below. Other entries in my blog will also shed some light on the subject. Most of the sellers interested in entertaining one of these transactions will already owe money against the property so they will not (should not) want to record any contact that might trigger the due-on-sale clause in their mortgage. Unrecorded contracts are difficult to protect should something happen to the seller, divorce, illness, death just to mention a few.
Finally, the reason most people seek this type of transaction is because they are not eligible from a mortgage from a traditional lender. Any work around to side step the mortgage underwriting guidelines shifts the risk from the lender to your side of the ledger, greatly increasing the odds of disaster. The guidelines are actually fairly liberal despite what most people believe. I have linked below some info on rent to own, but there are several other topics on my blog that may protect you. I hope my observations keep you away from harm, good luck.