The only way you can support your teamates as Enchantress is by keeling enemy heros.
You are not as item dependent and you can heal, thats why you're classified as support. Remember, you're a support that keels enemy heroes. Give your real carry plenty of space to farm.

Skills:
Pesky Impetus harasser throughout the entire game. (Always keep your distance. Use your carry as the meat shield)
Enchant is a dual purpose spell. Can be used to slow enemies and or show dominance to neutral camps, just like what chen does but chen is better at this. Dominated creeps are also useful as scouts.
Natures Attendants are simply repair drones that fixes its mothership enchantress and its allies. (Support with heals as best as you can, keep them teamates HP up)
Untouchable passive is cool when your enemies have no attack speed.

Reminder:
Maintain Ranged Distance, can't stress this enought. You're are not melee or tank, Position your self at a good distance.
Untouchable slow doesnt mean anything to hero's with attackspeed buffs or nukes.

Important Items:
Ring of Basilius = +1.5 mana regen keeps that impetus spam consistent at the early game.
Hurricane Pike = Force feed enemies with FAST impetus rainbows(item gives bonus projectile speed). Can be used to push enemies away from a teamate thats about to feed.
Witch Blade = Damage over time. Decent armor, attack speed and damage boost.
Aghs = Shoots 3 javeleins that sproinks you back due to its powerful force. (it has 4 sec cool down)
Shard = summon 3 repair drones that are tasked to constantly fix you or your teamate.