What steps do I need to take to hold the mortgage on a property I am selling?

You get a promissory note signed by the buyer, that pledges the property as collateral. Then you file a lien against the property using that note as security.

The note is signed at closing. You then tell the buyer what payments he has to make and when. You will need to create an amortization schedule because you will need to inform the buyer of how much he paid in interest each year. You will also have to file that info with the IRS.