DOTA 2 Basic skill: Placing Wards aka Warding
There are two types of wards in Dota 2. At the left side is observer ward and the right side is sentry ward. Observer ward is used to give a small vision in your map while sentry ward is used to detect any invisble units or heroes.
The red circle in the map above show the common spot for placing wards. Usually, we will use observer wards but sometimes, sentry ward is used to deward enemy wards or invisible units. The location near the river is important during early games because you can see if enemy heroes trying to gank you.
Deward. By placing sentry at the place where you think enemy put their wards.
Invisible hero also can be detected using sentry wards too.
Wards can be placed anywhere except certain locations. It depends on situation where you need to put the wards. Usually, just place it at the common spot is enough. Other spots are optional. Tips: Don't waste your wards because buying wards has cooldown, so use it when needed.
Another usage of wards is prevent pulling creep by the Dire by placing wards at the natural creeps camp. The creeps will not respawn because of your ward's vision. The rules of respawing creeps is spawn every minute when the camp is empty. So, yeah. Go to pulling creeps page for details. ;)