League of Legends (LoL) Question: Why is warding so important?

I'll try my best to answer ;-;
Wards play a huge role in league due to providing vision. Having vision of the enemy team gives you a huge advantage. It lets you take objectives if you notice the enemy is split up, lets you force a 5v4 team fight etc. Basically having map vision lets you further capitalize on enemy mistakes which leads to winning the game.

Everyone should ward. In the lane phase each respective laner needs to ward. In the case of bot lane the support usually wards. Jungler needs to ward his own jungle to avoid it being invaded or ward the enemy jungle if they're looking for invades. Come lategame, the support usually does most of the warding as the other team members make more use of the gold while buying items rather than wards.

Key areas that need to be warded depend on the game. Choke points in the map are the places that can provide a huge advantage while warded. The bush behind baron pit, bushes at blue & red buff, bush next to wraiths etc
Warding dragon and baron is a given.

You counter ward by either placing pinks or buying oracles and going to places where the enemies would usually ward. By destroying their wards you deny them vision and give your team an advantage. Again, common ward spots are choke - points on the map.
Note; place pink wards at the entrance to the dragon & baron pits. There might be wards placed at the back or sides of the pit just so you wont be able to notice them with pinks assuming you placed them further away from the exit, however, when placing green wards its better to place them a little away from the exit so that you gain vision of the enemy blue buff entrance.

You can test if an area is warded the following ways;
If I'm correct, when an enemy targets you they get a yellow outline. Which means if you're in a place clearly out of an enemy champion's vision range and they start glowing yellow, chances are that area is warded.
If you believe a bush is warded, whack a close by minion and see if it follows you in to the bush or resets after you enter the bush. The former means it's warded.

Sightstone and ruby sightstone are the most efficient ward related items.
They're used effectively by being bought early in the game and warding the already mentioned choke points. Its better to buy them early on because a ruby sighstone is usually enough to keep your lane safe from ganks and the more wards you place the higher the cost efficiency becomes.

Wriggles lantern provides a 90second ward that's mostly used for scouting and counterjungling. It has a shorter lifespan but can help keep vision of an area in a pinch.

Sightstone/Ruby sighstone should always be purchased on supports. The core support build involves Mobility boots and Ruby sightstone as the supports job is to provide map vision and these two items help with it.
Wriggles depends on the jungler and is not an item that's purely meant for warding so I won't bother explaining that.

• The ward provides vision of what the enemy players are up to. To spot incoming ganks, baron/dragon attempts (defensive) but also to spot players out of position (offensive).
• Everyone, perhaps with exception of the AD Carry/Marksman.
• Dragon/Baron, and preferably spots in the enemy jungle to spot for any aggression.
• Spot the enemy ward, pinkward that place and clear it (preferably with some cover). Make sure that you cannot get caught by people converging onto your position while warding.
• As a jungler, standing on the ward will usually trigger a reaction, often you can also just ask your laners if they have an idea whether the place is warded or not. Some other brushes (lanebushes) can be checked by looking whether minions attack you or not (if there is no vision, they won't)
  Often, you can also check for pinkwards using a sightstone stack if you are not sure (because they don't cost anything)
• Place as much wards as possible.
• Sightstone is #1 priority item as a support, so that should be rushed. Some other champions (like lee sin) can also benefit from a sightstone but that is limited to only these champions. Overall wriggle's lantern is a bad item and gets outclassed by all other jungle items so I would not recommend buying it.

Different enemy champions can necessitate alternate warding positions. Nearby river wards are of little use against a Rammus in Powerball, instead, deeper wards in the river and jungle are needed for adequate warning of incoming ganks. Junglers like Jarvan IV or Vi who can bypass common ward positions by jumping over walls also affect this. A purple team J4 can easily bypass a ward covering his blue buff entrance to gank bottom lane by jumping into the river bush, wards in the river bush are thus needed. This information also affects counter-warding; as the purple team bottom lane, leaving the enemy team with vision over the river but not the river bush can instill a sense of false security in less experienced foes if they are unfamiliar with J4's ability to jump into the river bush from the jungle.

Zac is capable of ganking mid from wraiths or bottom/top from within the jungle and can necessitate deep jungle wards. A Vision Ward in the middle of the lane can neutralise a Shaco who has already used his Deceive.

This also goes for late game wards. Keeping the nearby jungle warded when pushing a lane against a Fiddlesticks is important to prevent being caught unawares by a Crowstorm from the jungle, this is similarly useful to prevent surprise initiations from Hecarim.

Enemy behaviour may also influence warding positions. A jungle who frequently invades may gank mid from your own wraiths, which side bush or blue bush wards may not warn you of, in this situation it would be appropriate to ward in the ramp to wraiths.

Perhaps someone else could give other examples of behaviour affecting appropriate ward positions?

> Who should ward?

During the early game, every position should be warding (except for the adc due to the fact he has a support warding his lane for him). It is a common misconception at lower levels of play that the support should be the only person warding. This would be incorrect. During the mid to the late game everybody should attempt to buy a ward/wards every time they back.

The people who should be counter warding/Oracle users are most commonly the support and jungler due to the fact they don't need to rush their items (damage) as fast as the other 3 positions. An oracles should be bought when decently ahead or attempting to get ahead by ganking extremely often.

1. The main role of the a "ward", is to revel a small part of the map to your team, which otherwise would be clouded by the "fog of war". Wards are important because it shows enemy units, buildings, and champions, through out the map. Since the range of your sight, is general small, it is important to show the map so you can have "map control".

I'm tired so only one i really wanted to do

an idea for a question:
Are wards essential for champs like Teemo etc. that have traps that tell you where the enemies are?