Go to the Temple of Mara in Riften, and talk to Maramal. He'll explain it to you.
While wearing the Amulet of Mara you can buy from him, if an NPC likes you enough and has a marriage option, they'll express interest, and you're all set.
thanks for the info, a great help :celebration: .... any recomendations on who i should marry am a bit of a jack of all trades but like to sneak a lot.
If you marry Ysolda, she "owns" a shop - +100 gold a day. Not bad when you come back from adventuring to drop your stuff off, and get a complimentary 1500 coins.