Mods may vary, but you have a damage control team with slots. You can activate battlestations by hitting the battlestations tab, that will put your entire crew on active station. When you do this, all the crew in the sub light up. If you want, you can just activate your damage control party using that tab at the station. Depending on mods, you may have special ability crew that need to be in the right compartment.
The SHIV guide is a good place to start for learning the basic game and functions.
http://forums.ubi.com/showthread.php...The-SHIV-Guide