Suggested steps

1. Collect 20 obsidian blocks and create a flint and steel using the recipe
2. Go to the place you want your return portal to appear
3. Hit F3 while in the game and collect your X and Z coordinates
4. Plug them into this calculator
5. Equip some form of gold armor to protect yourself from Piglins. Zombies and skeletons are an easy source of early game gold armour
6. Use the first 10 obsidian to build a nether portal (2x3) and step into the nether (VERY cautiously)
7. Explore to the coordinates from the calculator. Again, be careful, the 1.16 nether is FAR more challenging to navigate than the overworld
8. Build your return portal at the coordinates shown, step through and with any luck you'll be back at the portal you built initially

Some specific cautions

◆ Dont get caught by very fast moving lava when tunneling in the nether
◆ Mining related falls are really easy if you are moving quickly
◆ Hoglins look friendly, but they are NOT. They will chase you and will kill you!
◆ One word: GHAST! They are foun everywhere but especially in soul sand valleys! Bring cobblestone to reinforce your bridges
◆ There's an enormous amount of lava. It will burn you up then it will destroy all your gear!
◆ Etc, etc, etc... there's so much to be afraid of in the nether. Be careful!

Nether Roof Portals (1.16+)

1. Collect 40 obsidian blocks and create a flint and steel using the recipe
2. Collect a ladder and some enderpearls. Follow the steps above. Once complete, netherside stair up to the nether ceiling
3. Dig around in the bedrock and look for a two wide area where the top bedrock is at Y level 127
4. Place the ladder on the wall right against the bedrock ceiling and enderpearl onto it and jump. Be patient, it takes practice.
5. Once above the bedrock, place a portal at the location provided by the calculator
6. Back in the overworld place your nether portal above Y level 100 at the corresponding coordinates
7. Test it out. You should show up in your roof portal. If instead you sync with a portal in the nether body, lower the nether body portal you just came through
8. Write down your nether roof coordinates! It is VERY easy to get lost up there!

Not Working?

There are some rare cases in which the gates might not hook up like you expect. If that happens, you may need to do more research to determine what's going wrong. If you stepped out of a new gate in a dark ravine or out in the countryside, recheck your coordinates. Stepping through a gate into unexpected territory is obviously jarring; So, be prepared. It's always a good idea to carry torches, tools, and supplies.
Note: If more than one overworld portal have the same netherside coordinate, the netherside Y elevation comes into effect. Simply place one netherside portal above the other. Fiddling may still be required.

Custom Nether Portals

for some added fun, here is a datapack to enable custom nether portals of any shape. simply drop the file into your world's 'datapacks' directory