This is a long, 4-phase encounter (in addition to which there are also 2 transition phases). Throughout the fight, Mar'gok will use the same abilities, albeit slightly modified in each phase.
Raid Guides
http://www.icy-veins.com/wow/imperator-mar-gok-strategy-guide-normal-heroic
Raid Guide Videos
https://www.youtube.com/watch?v=5q8Vsjcb_Ko - Normal & Heroic
If you have any issues or concerns regarding this or any of the bosses please contact either your role leader or one of the raid leaders and we will try to assist you as much as possible.
Regards
Lerouse
** Please note that this information has been copied and pasted from the guides themselves, I am merely trying to collate the information to ease the access to our guild members.