Supports are usually protective champions that are increasing their allies combat status and allowing them to lane for longer.But they have their jobs to do.
-Supporting carries
-Not allowing allies to die
-Warding
-Map control
-Debuffing enemies
-Disabling enemies
-Babysiting carry/tank/fighter/***asi
-Making sure your allies escape clearly

Shield is an very unique cast on support.
Once you cast shield on you or ally or at muliple allies if you are playing "Lux"
you or them will be protected from damage.

Heal is also very unique support spell.
Heal will recover your or your ally/allies(If playing "Janna") lost health.
Most of people think supports with heal are alot better then ones with shield becouse shield protects health but doesnt re*****h it while heal permanaltly recovers health.
However it is better early on in lane but when you have to react fast to save your allies maybe you wont becouse of:Ignite,some heal reducing spells,Graveyious Wound and stuff.

Only Sona has spells that create auras while adonitially you can buy items that create specific aura.

Most of supports have combat stats improving spells.
Combat stats are:
Attack damage
Ability Power
M/AD pen.
Movement.
Those champions are great teamate to your carry/offtank/assasin teamate for early game harrasment.

Supporting AD:Sona-Janna-Nidalee
Supporting AP:Janna-Soraka-Zilean
Supporting offtanks-Karma,Taric,Sona,Soraka
Map Awarness-Nidalee-Teemo

Start warding at 10:00min.Recall and bu< 2 wards.Place them in middle of river.

Claviyornace is support spell that everyone needs.
Why:You must make sure your allies dont die so you must reveal suspicious areas where your teamates might get ganked!You also need to look for easy kills in jungle.Search for junglers while laning so you enable ganks.Also if you have teamate like Ezreal reveal area where you think your enemy is so he ca send ulti in right direction.