The image shown here is of an unrepaired teleporter. Eight unrepaired (unactivated) teleporters generate in every newly-generated normal-sized and XL world. (In mini worlds, only three generate.) They are sometimes in dungeons, more often in specific types of unprotected bunkers.
A repaired teleporter looks like a narrow archway lit up with blue light. It is used for quick travel in a world. When tapped, it will bring up a map and you can teleport from your current teleporter to another blue teleporter or to an orange spawn teleporter. Teleporters are self-protecting. They are three blocks tall and two blocks wide, with no collision. You can find them in the Engineering section of your inventory.
Teleporters don't work until you activate them. To activate an unrepaired teleporter, simply tap or click it once. Activating teleporters helps you gain XP, get various achievements, and progress along the road to various Orders of the Crow.
You cannot destroy naturally-generated teleporters unless you're on a world that you own and you've placed a diamond mass teleporter in the world. The teleporters must already be activated for the mass teleporter to remove them, and the mass teleporter will remove all of them at once.
How to Obtain
You can buy a teleporter from the crowns store, or trade for one in a market world. They also drop as rare loot from mechanical chests and occasionally are offered as Daily Loot.
How to Use
A teleporter must be at least 50 blocks away from any other teleporter before you can place it. You'll receive an alert message if you try to place them too close together. Teleporters are a particularly important resource for people doing large-scale world projects, as they allow builders, and later, visitors, to easily jump from one important creation to the next.
For a long time, it was possible to use a butler bot to mine selected unrepaired teleporters in worlds that you own. Those teleporters would go into your inventory. Once the developers became aware of this exploit, the ability was removed.
Many players shorten the word "teleporter" to "tele" (pronounced "telly").