I'm still new and I'm in s4 and I've been playing for a year but i still don't know how to team fight as nidalee as she's my main. Do I stay with the ad carry and heal them and throw spears? Do I try to flank the enemy carry? What should I do?
First and foremost, don't teamfight as Nidalee.
She is horrible in it, so try to avoid it as much as possible. If you are forced into teamfighting_ (ie: the enemy team has Sejuani + malphite + orianna, thus not a good idea to leave your team to splitpush)_ your first job is to poke, from the flanks. You want to draw away enemy players. 1v2 you can handle, 5v5, not so much. Try to stay around, even with low HP, as you are a better bait that way (just be mindful of cait ult, and the like)
If the enemy did engaged to your team, don't try to peel, or heal the adc. In that (bad) situation, your job is to zone the enemy carries. Try to land a spear on an isolated target, go in for the kill, then run like hell.
you do everything you just said it just depends how the fight is going but mostly try to stay back and chuck spears and try to finish off low hp enemies in cougar if you can safely
Don't play that broken pos. Problem solved :D
Stay away from your team, off to the side, throwing spears from the fog of war.
If the enemy team tries to collapse on you as 5, run away while kiting them with spears looking for a kill opportunity. If you poke down the enemy team enough for a good engage, or your teammates land a clutch flash 
ulti or something similar, then jump into the fight and take out the backline.
Another way to think about it. Whenever you're up against an enemy Nidalee, what do they do really well that makes it hard for you to win? Do that.
Nida is not a team fight kind of champion. Her best role is in seiging towers with her team using her spears to poke enemies out of their defense so her team can take objectives. She is also a good assassin that can flank and split up enemy teams by landing a spear and making an enemy back or having some chase her so the rest of your team can engage with favorable numbers.
Stop worries about team fights and focus on objectives. Nida is a great split pusher if your team is smart enough to draw the enemy to the opposite lane and not engage unless they have favorable numbers letting you tear through the other lane and push hard Until the enemy responds.
During a siege you need your team to focus on poke and wave clear and sticking with the minion wavE. Not overcommiting to a fight under a tower but letting the pressure of minions do the damage as you poke poke poke the enemy away from defEnding. If they engage yoy need to as a group disenege. Never fight an even battle under a tower with a poke comp...disenege and look for a pic on an enemy that is our of position...then pounce. Now it's a fight in your favor. Tactics is the name of the Game. Tactics that focus on objectives....team fights are not an objective...kills are only a means to persue objectives.
