Bard is a utility focused job providing damage to the whole party with Battle Voice & the special buffs all of their songs offer. They excel in a multi-target environment due to being able to apply their dots numerous times. Here you can find the offical jobguide from Square-Enix explaining all skills.
If you prefer having a video version, below you find a short overview for Bard.
If you are just starting with bard I suggest the Bard beginner guide.
Just like every other job, Bard too, prefers Crit over anything else. The general meld order again is CRIT > DHIT > DET. The Best in Slot for Bard for Patch 5.2 can be found here.