You don't "introduce" cats to one another. Do that, and the cat will introduce you to his set of claws.
Ok, joking aside, we acclimated our cat to the expansive "world" by keeping him on a leash for a while. He was really young and cute, I remember, with big eyes and a determination to attack and kill anything that moved.
As for other cats... well, he wasn't a kitten. So I guess I don't really know. Our cat is extremely independent and attacked the other cats we had (until they died, probably out of terror).
Cats on a leash may look weird, but it's a great way to introduce them to the outdoors. The introduction to other cats may or may not go well depending on the cats. There's nothing you can do; it's not like they have to find out they have things in common to like each other. They either do or they don't.