As of right now, the gates are used to get deeper into the land, and as a method of traveling to the land dimensions of other players. Currently there are three gates in each land with different functions.
The First Gate[]
The first and second gate
This gate, along with the second gate, will spawn right above your house.
When entered, it will bring you further into your land, somewhere near your so-called land gate.
The Land Gate[]
This gate is currently spawned on top of a pillar around 500 - 700 (and possibly even more) blocks away from where you entered your land.
The land gate in a land dimension with the forest land aspect
When entered, it will bring you to the second gate of your server player. If you entered the medium on your own, it should just lead back to your own second gate.
Because of the drop, it is recommended to make sure that your server player have built up to their second gate before you enter your land gate.
The Second Gate[]
This gate is above your first gate. This gate is directly connected to your client player's land gate, (or your own if you are your own server player) and will teleport you there if you enter it.