The bar is the palce where you would manage your friends, your party, and also greet your friends. You may have up to 25 friends on your friends list. Here, at the bar, you can check up on your friends' information such as their level, offensive power, gender, elements on the weapon, rank points and their last login time+date. You can also see what their character looks like.
Besides being able to look at your current friends, you can also take a look at the friend requests you sent and the friend requests that you are receiving. These tabs are found above the friends list, allowing you to switch between them easily.
Another option on a button below is the 'Search' button. This button lets you type in someone's keycode in the box provided and to search for them. If it's successful, then it will show the target's information on the right of the box along with an option to add them as a friend if they are not already.
Now the last button is the 'Invite' button. This button is quite useful as you can use it to both find out your own keycode, and also invite people to join! Your keycode is a 9-digit number that acts as an ID# for your character. As the game doesn't have many real 'player-to-player' interactions, the game allows anyone to have any name within the letter limit. This means that multiple people can have the same name which is why there are keycodes to differenciate the players. On the right of the 'Invite' window, you can see a 'Bonus' box. This shows you what possible rewards you can get from inviting someone to Cross Horizon and getting them to type in your keycode at the beginning of the game.