Kartridge uses a mutual "follow" system to determine how profiles are linked.
If you follow another player's account, then you appear in their account as a Follower. If they follow you in return, then they are your Friend!
If you see someone in chat that you want to follow, expand the chat using the icon and click on the little person icon next to their name!
Kartridge and Kongregate friends are controlled by the same database, so you can find your friends from Kongregate.com on Kartridge easily!