Skyrim-HearthFire-Falkreath. How do you buy the house, and start and finish all quests?

I don't know all the details, but you need to wait and do some quests, and after a while, Jarl Siddgeir/Jarl Dengeir will send a letter, saying you can buy a house in Falkreath. It costs 5,000 gold, plus the expenses for building materials, a carriage, and animals. If you want, you can hire a Steward to furnish the house for you, at a great cost, around 15,000-20,000 gold total.