When you first log into the game you will be placed into a house with a vault and your wife and two children. Use WASD or arrow keys to move around. You can click on the mentioned objects once to pick them up, and then click again to place them down elsewhere. You have to protect your family and vault, and you start out with $2000 to do so.
On the top right you will see a cluster of buttons, this is how you select blocks to build with. You can see all of the placeable tiles in the game and their prices. Wooden walls are good to start with as they are cheap and simple; you can click on tiles in your home to change them to wooden walls, this change is not yet confirmed and money spent will be displayed in color below your balance before it is properly taken off. While the change is still unconfirmed you can remove them (by clicking again with the same tile or placing an empty floor on top of them) and have your money instantly refunded. It is as if you are planning out the changes to make. You almost undoubtedly lose whatever you make. Do not spend an hour making a massive house straight away, experiment and go out robbing first.
Your family needs to have a clear path to the entrance of your home. Pets can get in the way but no tiles can, even if you can walk over them.
So far you have been in build mode. You can not die and things such as wiring, pets and family are not active. When you're ready you can press "Done". This will initiate the self test. You have to prove that you can reach the vault of your house. You will notice that there is now a fog of war and pets are active. If you die you lose everything start from scratch again.
It's a good idea to experiment with how the different house objects work in robbery mode. You can kill yourself to get a fresh house and $2000 at any point. At this point you probably won't have too much to lose.
When you reach the vault in self test mode, thus proving your house possible, you will exit your house and be on the house list screen. You can still return to your house. If you change anything you will have to complete another self test to get onto the house list screen again (or discard the changes with "undo" or closing the game).
The house list screen shows all the currently available houses, all made by other players, and you can click to rob any of them. For other people your house is also on this list, available for them to rob.
If you reach somebody else's vault you gain everything that was in it. If you kill their wife and escape then you will gain the money that their wife had - the wife takes half of the house's money and tries to escape when she spots a robber. This is why it's best to keep your own wife alive.
Most houses will use tricks and traps to make them hard to rob, over time you can copy ideas for your own home and figure out how to bypass their defences.
If you go back to your own house you can also access your backpack to buy tools. These can help you to rob houses, but can not be used on self tests.
If you use tools while robbing a house and kill a family member or reach the vault, any destruction you caused will be permanent for the house. Although all houses have to go through a self test, past robberies like this can sometimes make a house impossible to get through without the use of more tools.
When a person dies at your house you get their bounty. Additionally, any tools they were carrying when they died get added to your vault. These can either be used or sold but will be stolen if another robber reaches your vault. You can also view your tapes to see attempts at people robbing your home.