Depots are a tool in the game, so that you can store items in a safe place while not using them. That is useful so that you don't run out of capacity at inappropriate times or by any chance die and lose most of your things. There is a depot located in every hometown except Rookgaard and the Island of Destiny. To use your depot box, simply go to the depot and open any of the many depot boxes.
Each city depot is unique: things you put, for example, in your Carlin depot will not be available to you in your Thais depot, and vice-versa.
Venore is currently the only town with 2 depot buildings, and you can access the same items from either of the two.
You can send letters or items using a parcel to your or another character's depot. For more information on that, check the Sending Parcels article.
There is a maximum amount of items each town depot can handle, and that limit is of 1,000 items for free account players, and of 2,000 items for premium account players. Of course, you can always parcel the items you want to a different city if a town's depot is full. You will still receive parcels when your depot is full.
When the depot is full (more than 1,000 items for free accounts, and 2,000 items for premium accounts), the following message appears in green: Your depot is full. Remove surplus items before storing new ones.
Also if you fill up the locker with 29 items, besides the depot chest, you cannot add more in it unless you remove items, or put some in another container. If a letter or parcel is sent, it will be there but hidden from view and use until items are displaced to make room. See this tip for storage ideas.