There are two major kinds of portals in Minecraft: The Nether Portal and the End Portal. To make a Nether Portal, you'll need at least 10 obsidian blocks and some way to light them on fire.

I start a new world, use creative mode to build myself a Nether Portal, throw away the key on the other side by destroying the exit portal, then slap myself back into survival. Lay it on me, lavaland.