Alright, here's the scoop. To use a gallery that you've created, put the following into the "page" or "post": [gallery=id]
Here's the catch. You need to substitute "id" with the number of the id of the gallery you want to display, such as "1" for gallery 1. So that means that to display a gallery with the id of "1", you would put the following in your "page" or "post": [gallery=1].
This is obviously different from how some of the template "tags" work, where "id" would mean that it was going to sort by id. As far as I know you can't have WordPress automatically find and display all galleries. You have to manually put each one in a "page" or "post", unless you were to write your own function to do so.