You cannot make an Enderman portal in vanilla Minecraft

Endermen do not have a craftable portal

To find Endermen, go to the Overworld at night, the Nether, or the End

To reach the End, build and activate an End Portal

Collect Eyes of Ender

Find a stronghold

Locate the End Portal room

Fill the portal frame blocks with Eyes of Ender

Enter the activated End Portal

If you mean a modded Enderman portal, check the specific mod’s instructions