How do portals work?

Hey everyone. I don't want to sound like a noob, but I am having a hard time wrapping my head around the nether portals I'm finding everywhere and how they work.

It's obvious that they are being used as teleport devices, but I just don't quite get how. How do you know where it points? Can you control where one points?

I've been reading another thread that said something about a correlation between blocks in the overworld and blocks in the nether. What is that correlation? How do I capitalize on it?

Just trying to understand better. If there is a wiki page that explains it all, just point to it please.

Thanks everyone.

Sticks

Okay so the nether is 8 times smaller than the overworld which mean 1 block in the nether is equal to 8 block in the overworld which is also the basis for nether portal transport. So if you walk 1 block in the nether that's 8 blocks in the overworld and so on. So if you make a portal at 0,0 in the nether (o,o in the overworld) and then make another on at 500 in the nether (4000in the overworld) you've pretty much just taken away 3500 blocks of travel time

Thanks Melk73, that makes sense. Can you determine somehow where a netherportal will point in either the overworld or nether?

Like which way it faces? I don't think so. You can determine where it will link to but I'm not sure about which way it faces.

So portals run of the theory 1 block in the nether is equal to 8 over world blocks so this is a efficient forum of travel u can link up portals which can be bad or be a obby farm

The way it faces has no effect on if it links

In single player, what Melk explained is really useful, and on here it's too, of course. But the downside to portals on EMC is that there are so many of them around already, that you often end up in somebody else's portal, while you want to make your own.
And breaking other people's portals counts as griefing, of course, so it can be difficult to link what you want together.
Note: if a portal isn't at the place it should be according to the 1 to 8, it checks some blocks around it, and if there is a portal near it, it'll teleport you there instead of creating a new portal at the exact coordinates.

Making sure your portals link together is easy. If your portal in the nether is at the coordinates in the overworld divided by 8 then they'll always link, granted they're on a similar Y level

Wow. Didn't know that!

Thanks everyone! This discussion is helping me a lot. So is some time I spent yesterday experimenting. You guys are awesome!