First you need to find a clear space in you world like I have
To make the portal you will need obsidian and flint and steel
Dig one block down in a straight line to make a base.
Add in obsidian into the ditch
Then stack the same blocks 10 blocks high.
Do the same on the other side.
Add blocks across the top to make a rectangle.
Select flint and steel and press on the bottom right hand corner with the flint and steel.then you portal should appear.
Tip:In the nether never lose your portal or you can't get back the the overworld.
The creator of this guide has not included tools