How to build a nether portal on minecraft

step 1 place 4 (or 2 if your using 10 blocks) blocks of obsidion on the botom row

add 3 obsidion to the sides

add 2 (or 4 if your using ten) to the top after you flint and steel the bottom row of obsidian the finished product should look like this

notice there is 6 blocks of actual open portal space