Supports are heroes whose purpose is to keep their allies alive and give them opportunities to earn more gold and experience. Supports will usually come with skills, such as healing spells or skills that disable enemies; and generally have low damage output (but often with a powerful-yet-situational ultimate). Supports are not dependent on items, and thus, much of their gold will be spent on items for the benefit of the team such as Animal Courier, Observer Ward, Sentry Ward, and Smoke of Deceit.

Supports are typically paired with the team's Carry at the start of a game. This is because the Carry tends to be the weakest and most gold-hungry member of the team early on, whereas support heroes are at their strongest in the early game.
A Support should always forfeit kills to any teammates who are more reliant on items than she/he is, only performing a kill if none of his/her allies are able to do it.

As support heroes do not rely on their right click to fight, they don't need all the expensive items that boost damage and attack speed. This allows them to spend less time farming, and buy team items like Observer Ward and Mekansm. Support heroes are usually at their most powerful in the early to mid game, while carries will dominate later on.

•What’s the point of Support Heroes?

Support heroes do not need items so much, so can afford to let the carries take what is available. This also allows them to buy team items, and instead of farming they'll be involved in ganks, pushes and team fights to buy their carries time and opportunities.

Author Notes : Is Bounty Hunter and Naga siren is a support hero on AGI? Of course no. But they can help our carry get more gold and exp on the lane. Also we can make Bounty Hunter and Naga Siren as a support hero. How? Bounty hunter has Track abillity , really useful. And Naga Siren has Ensnare that can snare the enemy. really useful.

• REMEMBER!
This is not hero item build , but this is guide for support hero items. Not main items build

One of the Main things that you need to Take Care in Dota 2 is supporting. Its one of the most important Role in Dota 2. First let me describe the wards.

There are two types of wards in Dota 2

• Observer Ward
  
• Sentry Wards

When you buy either you get a pair of wards. Which means that when you buy observer ward from the shop ( Price = 150 ) ( as on 19/4/2013) you will get a pair of observer wards. So you have 2 observer wards in your inventory

Observer Ward function :

• To give vision of large area.
  
• Helps you know enemy team Movement in the Map
  
• Block of Creep Camps ( if placed near / on their spawn site)
  
• Observer Wards are Good for high ground Vision.

Sentry Ward function :

• Sentry Wards give True sight Vision
  
• Sentry Ward is used to Deward enemy's observer wards
  
• It helps to see invisible heroes like Nyx Assassin, Bounty Hunter , Brood Mother etc

Some pictures of Warding and Dewarding

• Observer Ward ( Warding )

• Sentry Ward ( Dewarding )

• Arcane Boots

• Drum of Endurance

• Eul's Scepter of Divinity

• Forcestaff

• Heaven's Halberd

• Medallion of Courage

• Mekansm

• Necronomicon

• Orchid Malevolence

• Pipe of Insight

• Rod of Atos

• Scythe of Vyse

• Vladmir's offering