A balanced team usually consists of 1 semi-carry, 1 carry, 1 offlaner, and 2 supports.
A support can be a lane support or a jungler. The best support heroes for beginners are;
1) Lich king
2) Lion
3) Lina
4) Witch Doctor
5) Abaddon
Jungling support heroes
Crystal Maiden, Enchantress, Chen
When the game begins, the supports usually get the courier. If someone has already bought the courier (show-offs) or another support bought it, you should probably get some observer wards or sentry wards. (for dewarding or laning against invisible heroes)
Warding
Where to place them? You should either place them on the blue or pink circles not both. These wards can give you vision of incoming enemy attacks and keep an eye on runes and also if the enemy is killing Roshan. It also makes it easier for your mid-laner to gank. The purple circles give you a wide vision of the jungle which is also useful to anticipate incoming enemy ganks. Placing a ward on higher ground, will give you a wider area of vision.
If you see an enemy hero heading your way, use the alt+left click on them or where you last saw them to ping them out to warn your team.
Dewarding
To deward, buy some sentry wards and place them somewhere you think the enemy has warded. You can then take down their wards and earn some gold. Sentry wards are also useful for detecting invisible heroes. alternatively you can get a gem of true sight for dewarding and detecting invisible heroes. Just make sure your hero has a high survivability rate so that you dont drop the gem.
Shortcut keys for warning and giving commands
Hero is missing
Hold Alt and click portrait.
Hero is back
Ctrl + Alt + click portrait.
Defend/Attack Tower
Hold Alt+ click tower
Helping your carry
Pulling creeps
Stacking Creeps
