Flint and Steel
Flint and Steel function as a lighter. It can be made with a Iron Ingot and a piece of Flint. Place them side by side in your crafting grid to get a Flint and Steel. 
on a flammable material to set it on fire. Flint and Steel is ideal to ignite Nether Portals.
Bending Spacetime
To get to the Nether you will need a Nether Portal. For the Nether Portal you will need at least 10 blocks of Obsidian.
Build the portal as follows:
| Obsidian | Obsidian | ||
| Obsidian | Air | Air | Obsidian |
| Obsidian | Air | Air | Obsidian |
| Obsidian | Air | Air | Obsidian |
| Obsidian | Obsidian |
Now you have the frame for the portal. above the bottom Obsidian blocks with the Flint and Steel. Some purple stuff should now appear inside the frame. When you walk into purple stuff you will be teleported to the Nether. Beware, the Nether is a dangerous place to go!
The Nether: a parallel world
In Minecraft there are 3 dimensions: the Overworld, the Nether and The End. The first time you teleport to the Nether, the game will create a Nether dimension complety unique to your Overwold. The game will also create a Nether Portal that is closest to the corresponding place of the portal you used in the Overwold. The Nether is scaled down by a factor 8. This means that every meter you walk in the Nether corresponds with a distance 8 meters in the Overwold. So if you are far in to the game you can make a fast transport network.
The Nether is inspired by hell and thus is very dangerously. There are huge lakes of lava, flying mobs called Ghasts that shoot explosive fireballs at you, the burning Blazes that can set you on fire, Zombie Pigmen that can gang up on you if you attack them and stone throwing Wither Skeletons.