A lot of servers use a portals plugin. Here is a quick guide courtesy of Tannik Gaming Setups. Please diamond, and follow if you enjoy. Please comment if you would like another plugin tutorial.

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Step 1:
Install Advanced Portals (https://www.spigotmc.org/resources/advancedportals.21155/).

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Step 2:
Install ActionAPI (https://www.spigotmc.org/resources/actionapi.21879/).

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Step 3:
Restart your server.

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Step 4:
Log in to your server.

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Step 5:
Go to the area that you would like to put a portal in.

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Step 6:
Create a portal shape. It can be any shape as long as it is full walled in. (Image below)

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Step 7:
You can leave the portal empty, use water, lava, portal blocks or anything. If you want to use water or lava make sure to do /stoplag first to make sure the lava and water won't flow.

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Step 8:
Next in-game go to the location you want your portal to teleport to. Do /desti create {name}

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Step 9:
In-game go back to your portal and do /portal selector. With the iron axe you receive left click in the top left of your portal. And then right click in the bottom right of your portal.

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Step 10:
Do /portal create name:{portal_name} desti:{destination_name} triggerId:{portal_block} permission:{permission_node}
The permission node is optional

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Step 11:
Your portal is now complete! Go ahead and walk through it.

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