This thread is specifically only for this 3 methods of using a Sniper. Nothing else. I gonna explain all three methods, what the Pros and Cons are and when to use which of these methods.
Starting with the easiest of all.
Hardscope
Everyone can hardscope (hs) with a Sniper Rifle. Just tap the right mouse button and you're looking through the scope.
Harscoping is a save way to kill the enemy on a long distance, but not a save method when the enemy's close and you've not much space to operate. Why?
When you're scoping with an AWM as example you're zooming in with a factor of 2.8. Also the side's are black on the screen. You can't see what's going on in the near of you. The second scope factor is 8.0. You can aim more precise, but you see even less what is going on in the near of you.
Pros:
•Aim precise
•Aim for long distances
•shooting at the enemy will be most times end deadly for the enemy
•No practice required
Cons:
•Can't see what happens next to you outside the scope
•Moving slower
•shot goes anywhere, but not to the target you aimed for, when you move while scoping
Tip:
Hardscope only, if you know your teammates are keeping you back and sides clear or your enemy has no other way than coming in front of you.
Quickscope
Not everyone can quickscope (qs). It requires a lot of practice and the perfect timing of your fingers.
The name explains itself already, but you can quickscope when you press the right mouse button and immediately shoot after. You're doing a Quickscope when you can do it so fast that you even can't see the scope. Quickscope is the most common way to snipe for many experienced players. But Quickscope isn't a save method to kill the enemy, when he's too far away. It's like shooting ants with a needle while you're on the top of your house (except you live in a bunker).
Quickscope can be used with every sniper that immediately shows the scope when you're clicking the right mouse button. So not every sniper fits to do a quickscope with it, but the most common like AWM, Barrett M82A1 and M200 Cheytac.
Many players switch their weapons to something which has a fast draw animation like a melee weapon or even a grenade, which has the fastest draw speed at all btw. You can even switch faster back to the weapon with Melee weapons like Kukri-Beast or B.C. Axe-Beast (every weapon with the "quick Hands"-Perk is able to do it). Some weapons even require weapon switching because the reload animation is even slower than the drawing animation (M200 Cheytac, Barrett M82A1).
Quickscope is very handy, if you have close distances or the enemy could come from anywhere. Also you are able to see what happens next to you.
Pros:
•Able to see what's going on next to you
•Aim for short and middle distances
•Moves are faster
Cons:
•Practice required
•High rate of missing the enemy
•could end in a No scope
Tip: With a lot of practice you can even quickscope on long distances, so keep going, no one was perfect at the 1st moment.
No Scope
Finally the last method of scopes. I would say it's the most uncommon method if people aren't tending to fail their quickscopes so many times. It's pretty self explanatory.
No scope means that you're not using a scope at all. I'm not recommending this method of sniping since it has only 1 Pro and so many Cons.
Pro:
•100% when the enemy decides to dig his head into your weapon
Cons:
•99% of your shots will miss the enemy, when he's not digging his head into your weapon
•unnecessary wasting of time and bullets
•your team will kick you in 100% of all cases if you decide to play a whole game only playing with No Scope on a Sniper Rifle
Tip: Nope! Avoid playing No Scope. Just don't do it...
Hope this will help some players.
Greets and love
[Nyumi] 
P.S.: Gonna add some videos soon.