I'm trying to make this as easy as possible!

1. Open lib.php, change $keyId and $secretKey to the values given to you by Amazon.  
2. Drop the entire s3ui folder onto your web host. You can rename the folder if you'd like.
3. Surf to s3ui/index.php to start adding buckets and images.
4. The get.php is used to link your content into websites. For example:

If we upload 'myfile.txt' to 'mybucket' we use the following URL:

http://www.mywebsite.com/s3ui/get.php?id=myfile.txt&bucket=mybucket

It works, but it's too long. So in lib.php (line 68) you can set the default bucket,
and then when you use that bucket, you can exclude the parameter in the URL

http://www.mywebsite.com/s3ui/get.php?id=myfile.txt

With URL rewriting you can hide the .php extension, and by using relative links
the url lengths become reasonable. 

../s3/get?id=myfile.txt
