There are two types of wards in LoL that you can use. One grants vision the other allows you too see invisible champions as well. They are a single time use item that can come to your need when you least expect it. Wards are not visible to an enemy unless that enemy watches you place them or has a ward or oracle of their own.
Here is what the people at Riot have to say about warding:
Who – Most commonly, the jungler is assumed to place wards in high-traffic areas during the beginning stages of the game. Later on, tanks and support champions – ones who don’t necessarily scale supremely quickly with items – are typically called upon to buy wards.
What – There are two types of wards in League of Legends: Sight (Green) Wards, which are cheap, see far into the fog of war, and last quite a while; and Vision (Pink) Wards, which are more expensive, but also reveal invisible units. Sometimes there is a bit of a mini-game if both teams purchase wards: Buying the more expensive ones could allow you to kill the enemy wards while still revealing a sizeable area of the map.
Where – Wards can serve a variety of purposes. Vision Wards may be placed in the middle of lanes in order to look out for stealth champions like Evelynn and Twitch. Otherwise, high traffic areas, especially in front of Dragon and Baron Nashor on Summoner’s Rift, or near Grez and the Dragon on Twisted Treeline, are common locations.
When – If you’re most concerned with allowing the opponents to kill the significant epic monsters, you should ward their openings at their spawn times: For Summoner’s Rift, that’s 2:10 for Dragon and 15 minutes for Baron Nashor. On Twisted Treeline, it’s 2:10 for Grez and 4:30 for the Dragon.
Why – Wards will allow your team to gank enemies as they attempt difficult objectives like the Dragon. Additionally, placing them in high-traffic areas allows your team to protect themselves from being ganked.
Clever Uses of Wards – As mentioned in an earlier topic, champions with unit-targeted movement spells may target wards with abilities like Leap Strike or Shunpo. Additionally, certain abilities like Gangplank’s Raise Morale need to target a friendly minion. Carrying a Sight Ward in your inventory allows you to Raise Morale at a moment’s notice.
Also keep in mind that many champions have abilities that allow them to place objects similar to wards. For example Shaco can use his Jack in the Box's to slow down enemies and alert allies that an enemy is on the way. Other champions, such as Te Emo and Caitlyn may also place their own wards which they can use to monitor their enemies movements and possibly set up a gank of their own against a lone champion between lanes.
I would also like to emphasize the importance of killing the dragon on Summoner's Rift. Killing it provides every member of your team with a significant boost in gold (about 200) and also grants additional XP. While the dragon does not offer a buff (on Summoner's Rift) it can provide your team with an extra 1000 gold that can put you far ahead of the enemies. Keep this in mind when playing.
Note, however, that a ward near the dragon can result in many easy kills. Usually a champion will attempt to grab the dragon as soon as possible to make sure that you (the other team) doesn't get it. A ward placed near the dragon can make for an extremely fun steal or kill.
Finally, when fighting Evelyn. Do not buy an oracle at level 1. This is a waste of your gold. Instead use the gold to purchase a pink ward. Place the ward in the center of the lane and your golden. Eve will be visible and you will have an extra 300 gold that you would have spent on an oracle. Also note that wards do not die when you do, Oracle's does. If you do want someone in your lane to buy an oracle make sure it is the tank as most other champions are easily ganked and then you lost your 400 gold oracle.
Hope this helps and good luck out there.
