Hello, I'm Tsunami10, and I am a main support with Sona. There are starters that keep asking what a support does, buys, and other stuff. I'm here to show what I know about them, so if I miss something, message me and I'l update this guide :3.

What is the support ? What is his function ?
These are the basics things about a support:
It stays on the bot lane with the ADC, helping him on killing the enemy ADC and protecting him. He don't farm, or get kills: it goes all to the ADC. Why ? Most of the supports don't have the power to kill, so it only protects the ADC. What a support do that is important ? If you didn't took the protect ADC meta seriously, choose other lane: the ADC is essencial on team fights, and he must have the build and good level to cause damage. But, taking the ADC protection off, you get to ward the map: vision of the map is essencial for your team, in order to don't die or let the other team get the dragon/baron, steal blue/red, and others.

What champions are supports ?
These are my recomendations for supports :
For healing champions, pick :
Sona, Soraka.
For tank champions, pick:
Leona, Braum.

ATTENTION : The champions I listed above require some practice, so I recommend playing against IA for the first time.

Where should I ward?
Just a tip : Ask for your jungler to ward : your blue and your red. Ask for you top to ward : Baron.
Where do you ward ? You should ward :
Dragon; Baron; River; and lane.
Warding your lane is good, because if enemy advance, you can know where is he going. Situational Example :
You and your ADC are at the mid, at a team fight, but the enemy ADC is at bot lane, taking the minions out. There is no ward there, so you can't see him when the last minion is killed. Then, your team thinks he is advancing to the tower, but he's not : he is going to the mid, ready to get your team by surprise. It is so fast, but you hear : ACE, your whole team was killed. The enemy team advance through the lane, take the inhibitor, and later there are the red, big letters on your screen : DEFEAT.
See the importance of wards now ? Yes, but what do I buy ? Depending on the support you are, there are items that offers stats and wards, such as Observator's Eyes.

When I ward ?

That's a good question.
When the game starts, pick a warding totem and pinks. Rush bot, ward the bush at the river and the bush at the lane, the enemy one. That's a good start.
The best moment to ward is when your ADC is at base, and their ADC/SUP is off too. You shall not farm when this is happening, you must ward.

Basic Rules of SUP

Don't farm when ADC can farm.
Don't kill, unless no one can.
Die for your allies.
Buy and use support items.
THE SUPPORT HAS A DIFFERENT KDA : Assists count as kills, o if you are 1/10/23, you should count it as 24/10.

[This part is under construction. I'l update it as I get more experienced with support roll]