I'm the worst player in PvP

[Astrophysx]

I tend to get bewildered and freeze up as MNK when a big engagement starts, because I'm really not sure what I'm supposed to be doing. I know I'm supposed to kill things, but I'm not sure how I'm supposed to do that correctly.

XD It's okay.

Anyway, PvP (in all modes) is very different from PvE. For a start, you should learn how to BURST. PvE style rotations are okay. But if you really want to kill targets, you have to know how to burst. What bursts do - If coordinated with another DPS, it will 100-to-0 a target almost instantaneously. If you're trying to solo kill a target, a burst will increase your chance of a kill on a target with 50% or less HP.

The Wolf Pups Den Discord (although centered on Feast) is a good resource. I recommend joining and asking questions about bursting with MNK or whatever you want to learn in the "melee questions" channel. Since I'm not too familiar with MNK's burst, I can't tell you how to do it (although I know that Forbidden Chakra and Tornado Kick are definitely used in it). However, there are top tier PvP vets in that Discord that can tell you how. ^_^

UPDATE:
Just some tips for Frontlines:
- Don't attack targets with their healer around... if you don't have your healer around.
- Attack targets that doesn't have their healer around... if you have your healer around (unless you're good at 1v1)
- Don't tunnel vision a target into a trap.
- Always be aware of the objectives... and go after them.
- Always try to get Battle High/Battle Fever.
- Don't attack jobs with push-back abilities at the end of a cliff (MCH, WHM, SCH - they will push you off... and you will die).

Anyway, hope this helps. Good luck!