How do you get to the nether in minecraft?

You must first build a portal with obsidian. Obsidian is made by pouring water NEXT to a source block of lava so the water flows into the lava. Be careful not to pour the water directly onto the lava. You will want to make a mould out of cobblestone to make it easier to get the obsidian where you want it. If you mess up the obsidian will take a while to be mined, so be careful. This is a very hard idea to explain so this model should help.
O = Obsidian
_ = Open Space

OOOO
O_ _O
O_ _O
O_ _O
OOOO

Like I said, this is very confusing, but after some trial and error, you should get it right. After the portal is made, you must use flint and steel to light an obsidian block. Once lit, the open space will turn purple and when you step inside your view will begin to swivel and a loading screen will appear. After loading you will be in the Nether. To leave, simply step back into the portal.

Tip: The corner blocks don't have to be obsidian. They can be cobblestone, dirt, empty space, whatever. So you only need 10 blocks of obsidian to create the portal.