do you want to add an attack to it?
if so, create a weapon for it and then equip it on the Unit information where you can change life armor etc.
its explained in that Unit tutorial, decide which weapon you want it to use and then either equip it without changing it, or recreate it if you dont want any changes you make to it to effect its host.
i.e. if you equip the marine weapon to your medic, then change its dmg all marines will have more dmg as well.