From Astroneer Wiki
Tether is one of the items in Astroneer that can be crafted via the backpack. It is an essential item to have throughout your playthrough, especially in early exploration. One Compound provides an entire stack that holds up to 11 tethers.
- To place a tether, press the T key (on keyboard) or bottom of the d-pad (on console) to drop a tether at your astroneer's feet. The tether can then be dragged into the desired position, and can cling to walls or ceilings. Note that tethers must simply be within a radius of each other to connect; they do NOT need line of sight with each other.
- A tether line will be created between two tether posts that are close enough. When dragging a tether, a transparent dotted line will show to which tether the new one will be connected to when released (if any).
- Tether lines will be blue when connected to an oxygen source or dashed blue/yellow when power is also flowing toward a player.
- When the tethers are not connected to any base or vehicle, the tether lines will be black. In that case, the player won't get oxygen or power from them.
- Vehicles can link to tethers, but they will only act as a source of oxygen, unless the vehicle has a power source. If the player runs out of power while tethered to a vehicle, the vehicle's internal power will begin to feed to the player without recharging their equipment.
- Only the player can recharge their power through a tether. Vehicles and bases will not receive power. However, one can charge a Small Battery and then place it onto the vehicle/base that needs power.
- Once placed, tethers can be picked up again and put back in a tether stack (or empty slot, thereby creating a tether stack) by clicking on the stack in the backpack. Shift-left-clicking (on keyboard) or pressing X (on xbox) on a tether while holding it will automatically return it to the backpack, assuming there is space for it.