The social bar is where you find all your social connections in the game.The first tab with 3 top arrows is the neighbourhood bad. By taping your portrait you will be able to change it. If you tap on another player portrait you can interact with him. If you visit another player city you will be able to polish, motivate or plunder (if you fight against him and won) any of his building. If you tap on motivate, you can choose any bulding with a grey star on the top to motivate.
The second tab with a shield displays your guild members. There you can also open your guild window. If you currently in no guild, guilds will be displayed there.