How do I add someone to my Buddy List?
When someone is on your farm, click on their avatar and choose the option at the bottom of the pop-up that reads "Add to buddy list"  The user will receive a message asking if they accept your invite to be buddies.
How do I visit buddies?
Click the "buddies" at the bottom right of your game screen and a list all your buddies will be displayed. 
Click on the name to send them a message. 
Click the single green man to go to their farm. 
 If a double green man appears next to their name it means that they are online. 
Click on the bulldozer to remove them from your list.
What is the Buddy List?
It allows you to contact people who are not your friends on Facebook & visit their farm plus easier to contact then and hire them if your neighbours aren't online..  You can also send a FC gift to a Buddy.
When a double green man appears next to their name, one of your buddies is online.
Clicking the icon will bring up two options..
a) Join 'User': Sends a message to 'User' asking for its permission, if user accepts, you will navigate to where that user is located.
b) Ask 'User' to Join You: Sends a message to 'User' asking if he/she wants to Join You. If user accepts he/she will navigate to where you are located.
These options work in every place, you or the other user can be anywhere, including farms, marketplace, Realtor or inn.