How Do I Make a Hell Portal in Minecraft?

Place four blocks of obsidian on the ground in a straight line.

Place a block of obsidian on the first block in the line and a second block of obsidian on the last block in the line, leaving two empty spaces between them.

Place two more blocks of obsidian on top of each of the two blocks you placed in the previous step. You should now have a four-block-long line of obsidian with a three-block-tall column at each end.

Place four blocks of obsidian in a line on top of the columns, connecting them. You should now have a four-by-five block frame made out of obsidian, with a two-by-three empty space in the center.

Light the inside of the frame using a flint and steel. This will replace the empty air inside the frame with a purple, swirling material, activating the portal.