In Seller Financing, you would expect to own the property, encumbered by a loan and deed of trust.
You would be an owner.
Rent to own is undefined, but you would not own until you finance or pay the purchase price.
You would be a tenant.
Do not venture into either without legal counsel from your own attorney. These are not arrangements that can be properly done verbally or by laymen, or that you should enter into casually.