The Bottom bar is the toolbar at the bottom of the screen and contains a series of useful tool menus.

On the top row are:

Chat & Trade windows: Your main source of direct communication with others. See Chat and Trade article for details.
Building Menu: New system for building and demolishing structures See Building Menu article for details.
Economy Overview: Display information about your building materials, food, etc.. you produce and consume.
Scales: Trade Office. Allows you to buy and sell items from other players.
Star Menu: Your Professionals, Buffs and won Resources. See Star Menu article for details.
Interface Arrow: Below the Star Menu is an arrow to show/hide the lower Interface.
Guild Menu: To help you find and manage your interactions with the Guild. See Guild Menu article for details.
Email: A big icon to easily open your mail. See Email article for details.
Store: The home of premium and Event related content. See Store article for details.

On the Lower row are buttons for you managing your friends and a useful Home button to get back from Adventures.

At either side are arrows to move up and down your friends and the buttons just inside that on the right are to filter those friends between All, Just Friends and Just fellow Guild members.

Seet the Friends Section for more details.

The three buttons on the left side are, in decending order:

Find and Add Friends
Click this to get a little window to type your existing player friends names to locate them from the list and Send them an email offering to become friends. On acceptance their portrait is added to the central bar of faces.
Invite Via Email
Inviting friends from outside the game to join is a basic and in TSO you can get a reward for doing so. If the new player purchases items with gems from the Stores (not using gameplay gifted Gems ) the inviter receives 200 Gems.
Return Home
Extremely handy as a way to easily get home from visiting a friend or an Adventure.

The final part is the list of friends you have made which is sorted by Level and then Alphabetically. Clicking on their faces brings up a menu to visit , trade and remove them.