For every house (and for example, a ship) that you acquire, you will receive a key. It only works for the object to which it is attached, for example, the front door. As the owner, you can lock your house and no unauthorized person has a chance to get in.
There are a number of keys, which can basically be divided into magic keys and other keys. Magic keys have the property that after the death of the owner, they do not remain in the body, but with the players "ghost". In order for the key to work magically in this way, it must not be stored anywhere other than in the main backpack. You can give the magic key, like other keys, to another player.
You can obtain the Magic Key either when buying a house from the GM, or have it made by the Tinker. The newly acquired key is, however, "blank" - clean and must be copied. You do this by double-clicking on the original key and then on the magic key. If you have more keys, it is also a good idea to name them by double-clicking on them. This copying procedure also works for other types of keys.
If the object to which the key was bound ceases to exist, the key becomes "blank" again, i.e. empty.
If your house door is locked, there is no way to open it without a key.
The player can make a lockable chest (or other thing) himself using the Lockkit, which can be made by a tinker. This thing can also be pryed open using the LockPick.
Up to a certain distance from the house from the deed, things can also be locked to the ground so that they cannot be taken away. You use the original house key (2 x clicks) and the thing you want to lock (1 x click).
If you have more keys, you can put them on the Keyring: drag the key onto the ring, double-click back on the bundle and target the ring again. The Keyring is also a so-called newbie item, i.e. in case of death, it remains with the "ghost", not with the corpse. This is not 100% true if there are also non-magic keys on the bundle.