Here's how you get the latest experimental code:
(if you know what Git is you can get it that way too).
Gallery needs a place to stick your photos, so do this:
Then point your web browser at the gallery3 directory you just downloaded. You'll see a page which looks like:
The only thing you should need to enter here is the user name and password for your MySQL database, that you must create yourself. More detailed directions are available here
If you don't know what's going on at this point, try clicking continue.
If you get an error that index.php cannot be found, you need to do 2 things:
After the install, you should be logged in as the admin user. Here are some things to try to get you started:
If you cannot add a photo, you need to install G3 Plupload module or html_uploader module into the Module Directory.