Sniper is easy to understand, but harder to master. Sniper's role in hit game TF2 is being annoying OR being lucky as hell.
This guide will talk about LUCKSMAN and normal piss master god 2009

So to shoot its pretty easy, You need to press M1 at the enemys head while scoped in and they will 99% die (The 1% is vacc medic pocketing them with uber)
And to NOT die, after shooting crouch then uncrouch. this will make the enemy sniper mad

So this part will be long as hell. Good luck reading!!

Scout => These ♥♥♥♥♥ are fast as hell and will try to off your aim, Just aim at a part. they will walk into it and shoot.
Soldier => These dudes are NEW or 5k hours, If this dude is new. Just aim straight at their head and they will die. BUT if its a 5k hour one, good luck just try to use ur secondarys too.
Pyro => Use god tier weapons like jarate or the most infamous "♥♥♥♥ you pyro" secondary Darwin's Danger Shield
Demo => Just stay away and shoot them, if they are close. Melee them because if they hit u, they get damaged by the explosion
Heavy => Stay away from him like demo, if hes close, quick scope his ass.
Engineer => This dude is easy to beat. Just be away from him OR go secondary and melee on his ass. Or if ur feeling a bit "SPICY" you can just quick scope
Medic => This class is easy to beat if ur not in his melee range or primary range. If ur in his melee range, pray to Gaben to not get random critted every hit.
Sniper => This is just luck and skill based fighting theres nothing to say.
Spy => Just use Razorback OR just quick scope him.
This area is done.

So I will start with the bows.
Huntsman and The fortified compound => They are the same, use this if ur feeling LUCKY
Stock, aussie and AWPer=> They are the same, the differences is 1 is shiny and gold. 1 is from CS:GO
The Classic => Never use this piece of garbage like a normal rifle, Just hold M1 and stop holding when an enemy is on ur crosshair, NEVER EVER USE M2!!!
The Hitman's Heatmaker => This is REALLY good for MvM, good if the enemy team likes cuddling with eachother (Staying together)
Sydney Sleeper => Use this to annoy the enemy snipers and the spys. This gun can extinguish fire if u hit your teammates that is burning.
Bazaar bargain => Use this gun when u can hit your shots or enemy is just stupid and doesnt know how to throw your aim off