First, you need to actually construct the frame. This is by default identical to the rules of a nether portal, i.e. a 5x4 rectangle of obsidian blocks with the corners optional.
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Second, you need to put a sign on one of the two center blocks of the sides (highlighted with a * in the diagram). This sign will describe the gate.
Here is the sign layout:
Line 1: The name of the gate. This is what is shown on the gate and in dialers, and must be unique on its network. It has a maximum of 11 characters.
Line 2: The destination of the gate. If you provide a destination, it disables the dialer and links to only that gate.
Line 3: The network of the gate. Gates can only access other gates on the same network. Under the default Stargate configuration, this will default to
central if unspecified.
Line 4: Gate options. Can be any combination of
A: Always-on. Requires Line 2 to be set. An always-on gate does not have a button and does what it says on the tin. It also removes the gate from dialers.
H: Hidden. A hidden gate does not appear in dialers, and cannot be accessed by players other than its creator.
P: Private. A private gate is the inverse of a Hidden gate - it can be dialed to, but cannot be used by other players than its creator.
F: Free. If economy integration is enabled, a free gate costs nothing to use and - by default - costs nothing to dial to.
B: Backwards. A backwards gate exits from the back.
S: Shown. If Always-on is enabled, this shows it in dialers anyway.
N: Network Hidden. The name of the network is not shown on the sign.
R: Random Destination. The dialer is disabled; instead, when the gate is activated, it leads to a random gate on the network.
Once you’ve exited the sign, the portal will finish setup. A button will be added to activate it.
To use a gate with a dialer, right click the sign to turn it on. If economy integration is enabled, free gates will appear green by default. Right click to go forwards, left to go backwards, until you select the gate you want to go to; then, push the button and the portal will activate. Once through, it will deactivate again. If the portal does not have a dialer, simply press the button to activate the portal.