The portals are made by creating a 4x5 (2x3 on inside) door frame out of obsidian and then lighting the inside of the frame on fire with Flint and Steel. The corners of the frame may be left out, using only 10 obsidian. When you stand inside the portal for the first time, it will create a portal in its equivalent area of the Nether. A loading screen will appear during the change of worlds.
When re-entering the normal world, any distance covered in the Nether is multiplied by 8 times, effectively making the Nether a fast travel zone that allows for greater distances to be covered in a short amount of time in the normal world.
Portals can be walked through. In order to use them, the player has to stand still inside the purple haze. Currently, they won't transport mobs or mine carts. Attempting to go through a portal while in a mine cart will result in the player needing to restart the game to continue.