The tanks role is to take damage and taunt (keep the monster attacking said player)
the tank should have most points in his vitality attribute so he gains more health points
there are some strategies to tanking such as standing away from the monster and taunting so you do not take melee damage (physical damage) and will only get hit by the monsters magic attacks, this strategy will occur with mainly: deadroot, shimmerspell or starspell, shivercowl, fellfire or charfire, chillmist or crystal mist, bladewing.
tanks will mainly use a shield and meteoric sword (or any other weapon that gives a health bonus or makes tanking easier) as it gives a health bonus but that is optional, the tank should put skill points into: protective stance, enduring guard, taunt, i would only give warcry a few points but it can be helpful at times, rest of the points are optional.
a tank wears heavy amour, armour decreases the damage taken and defence gives you a chance to dodge the enemy's auto attack (non skills hit) some tanks use a mixture of defence (dexterity) and vitality but a pure health tank will just use all vitality, but it is common for a tank to put most of his points into vitality and use some strength. Some balance of vitality and dexterity is probably best to stay alive longest if the tank is standin close to the target, but a pure health tank may be desired for monsters that will cast spells while the tank is standing out of melee range.
the tanks enduring guard skill helps to evade the enemy's skills hit and protective stance gives you more armour depending on its level, the tanks shield bash can be a very useful skill but other skills such as taunt and stance come first. tank rotation, this usually occurs when there isent enough druids and there are 2 tanks online, one tank will take hits until he has low health and then the 2nd tank will start taunting, when the 2nd tank has the agro (attention of the monster) the one druid will heal the first tank, once then 2nd tank has low health the first tank will taunt and then the druid will heal the 2nd tank, this will continue until the monster is dead.