Instead of playing as Master Chief you play as an elite. You have other elites on your side, fight spartans and marines. Note: this is for Halo PC (Combat Evolved) not Halo CE( Custom Edition )
After you saved some elites in the level halo the grunts have captured your elite captain. You have to lead your elites in the grunt ship and rescue your elite captain. This will be porbably the last time you will be fighting grunts but again do not underestimate these little guys. Their tougher than you think!