To pick the lock on a chest or door you first need a lockpick set, which you should wield in one hand while assisting with the other (see ‘help assist’).
You should then target the chest or door you wish to open, using your assisting hand to perform the available techniques. Every time you perform a lockpicking technique, the lock will make a sound to indicate the state of its tumblers; a clUnk means that the tumbler is under the desired value, a clOnk means that the tumbler is over the desired value, and a click means that the tumbler is correctly aligned. When all the tumblers click, the lock will open.
Each technique (except for probe) will move one or more tumblers by one or two positions in a direction - ‘>’ increases a tumbler by one, ‘«’ decreases a tumbler by two, and so on. Each of the three lockpicks has different available moves, and you’ll usually have to use them all to open a lock.
If you try to move a tumbler too high or low, the lock will jam, meaning your lockpicking technique failed to do anything; try using a different technique.
The chest must be lying on the ground in order to be opened. The safest way to do this is to drop the chest in a store on your home plane, where it autosaves.