If you want to get the hang of captain, you should know a good knowledge of its strengths and weaknesses. So let us take a quick look at those right now.
   When it comes to strengths for captains, they do medium to high damage, consistently. They don't do as fast damage overall in shorter fights. But when next to a hunter and champion (who do fast damage in quick fights) they will actually hold their own, damage-wise, over the long haul, especially if they equip traits in the damage line.
Hunters and champs need to put the enemy down fast or they will soon find themselves on the back foot. They tend to find they change from the offensive to the defensive in longer battles, whereas a captain will remain consistent in his tactics, and still have the ability to sustain himself well over a long fight.
Captains can wear any armor in the game, so they are well protected. They cannot use a heavy shield like the guardian, so they won't have quite the same armor value. But they certainly are able to stand toe to toe with any foe within their league, especially since they are able to swap out their two handed weapon for a one handed weapon and shield, and suffer no major penalty to their stats, performance, or their main role, like guardians and champions would.
Captains are arguably the most versatile class in the game. They have as many tactical (non-physical) attacks as they have melee attacks, and they even have a few, clever ranged tricks at their disposal, if necessary.
   When it comes to the weaknesses of captains, they have the least amount of ranged attacks out of their arsenal of tricks. They can pull with a couple of shouts, and one of their marks. And it isn't actually until level 56 that they acquire a range-attacking herald, so they suffer a little in this area.
Captains can't innately hold aggro very well, which may limit their ability to tank efficiently, though they can compensate for it by a number of useful traits introduced in the Mines of Moria expansion, and if they work a little harder by using skill chaining tactics and certain buffs.
Captains are quite complex to play effectively, so players who like simple characters will often find there are too many things to concentrate on at once.
   For the most part, captains have many roles in a group such as buffer, healer and the like. Let us get started with those two roles.
   As buffer, captains can give you buffs that provide extra attack speed, HoTs, boosts to all stats, extra percentage to crit and extra percentage to parry, they give extra morale and resistance to fear. Captains provide the absolute best group buffs out of any class.
   But as healer, they are excellent backup healers. While their healing isn't as good as a minstrel, and they are often needed on the front lines, they have quite a few special, background healing skills, such as a HoT which is applied to an enemy in the way of a Mark--and all allies who attack that enemy gain this HoT. They have a spam heal which can target only one member of the group at a time, but is very fast, and traited, can heal fairly well. And they have a very good heal that comes into effect when an enemy is defeated which adds a HoT. These are just some examples of the many lesser and greater ways a captain can heal.
   Captains add the extra edge to any group that want to not just survive but actually do well while not necessarily excelling at any of these roles.