Go to the S3 console and click "Account" at the top-middle.
From there, click "Security Credentials"
Create a new access key or use the default one. You will need to enter the two keys into the SocialEngine adminpanel.
Go to the new configuration page in the admin panel under Settings -> Storage System
Click on "Add Service"
Choose "Amazon S3"
Enter in the information from the Security Credentials page in (fig 4) and choose a region. The region should be closest to where you think your users will mainly be located. Be sure to click "enabled"
To set this as the default storage service, click the default button. Files can be transferred by clicking the transfer link (this make take quite a while depending on how many files you have. This is done using the tasks system and is run in the background).
CloudFront is an actual CDN, while S3 is just cloud storage. Here is a Wikipedia article on CDN Benefits.
The steps above must be completed prior to enabling CloudFront support.
First, a CloudFront Distribution must be created from the bucket used above. It may take quite a while for this to become usable!
Once the distro says "Deployed" under the "Status" column, copy the "Domain Name" and enter it into the field (as shown in Step 8 above).