Those are two genuinely different structures, so you're not confusing yourself for no reason.
The more common one, and the one this room is mostly about, works like a regular sale. At closing you deed the property to the buyer. In exchange the buyer signs a promissory note, which is the written promise to pay you a stated amount at a stated interest rate on a stated schedule, and a deed of trust or mortgage, which is the document that ties that promise to the land so you can foreclose if he stops paying. He owns it. You're the lender.
The other one is the land contract, sometimes called a contract for deed or installment land contract. There you keep title and only deed it over after the final payment. It sounds safer for you, and in some states it is faster to unwind, but in plenty of other states courts treat a long-running land contract much like a mortgage and make you go through a full foreclosure anyway. Which one is better for you depends entirely on your state's law, so that is a question for a real estate attorney in your state, not a forum.
On who writes it: not your agent. Agents generally can't draft notes, and you don't want a form off the internet securing eight years of your money. An attorney draws the note and security instrument, and the security instrument gets recorded with the county so the world can see your lien.
One thing to settle before you agree to anything: what happens to property taxes and who is responsible for proving they got paid. On vacant land a buyer can stop paying taxes long before he stops paying you, and a tax lien sits ahead of your lien. Most notes require proof of payment each year for exactly that reason.
