By being part of a squad, you are automatically awarded a temporary rank that is used for personal skills and abilities. Upon joining or forming the squad, you will gain this rank by either going to an armory or barracks and changing out your kit. While in a squad you can see your squadmates name, health, ammunition, and action status in your HUD. When a squadmate is under attack it will flash red, when they are attacking it will flash yellow. If your squadmates are to die in combat they will appear with red X's over there names.
Joining or Creating a Squad
Joining or Creating a squad is done via the Pop-Up menu. The default binding is the F key, which will show something like this:
From there, you can either press S or click the Squad Menu with your mouse. You will then either be able to accept a squad invite or form your own.