LoL... Because why not?

I can build on what Reli stated, I main Support most of the time, so I'll provide on that.

Support is the other guy in the duo bot lane, along with the ADC. Usually tasked with the warding and protection of carries. Support's role is kinda like CB's, help the team with heals, crowd control, buffs etc. In lane, you'd want to babysit your ADC by healing him, buffing him, having a presence so that he can farm easier (not just sitting in a bush), make plays to get him fed (if possible) and to ward the surrounding area so that anyone roaming to bot lane doesn't screw you guys over.

Tips as a support

• Don't take cs. This contradicts what Reli said in his post but there's a reason for it. Usually the ADC, not you, is gonna be the one dishing out damage later on, therefore, you shouldn't take the cs so that he can get his damage items and stuff faster.
  

• Don't take kills. Other than getting verbally bashed for it, the gold gained would be better on the ADC rather than you in most cases. Of course, you should take it in various circumstances, like if you know you can get it after your ADC's dead.
  

• WARD. Although each team member has the responsibility to ward, most of it falls on supports. Places to ward off the top of my head: the river area near dragon, tri-brush. Wards provide vision, alerting of ganks. Later on during the mid and late game, you'd want to be warding the area around objectives like Baron (worm) and Dragon. A good item for this is the Sightstone and its upgrade, Ruby Sightstone
  

• Having a presence. Don't camp in the brush forever. If you show them who's boss by poking at them or running at them as an aggressive support (Bitchcrank, Leona, Thresh) or poking them with things like Sona, Lulu, Annie, Zyra, they'll be spooked and back off, giving your ADC more breathing room (most of the time). Of course, there's certain things to take note, like who the enemy support is. e.g. if you go too aggressive as a squishy like Sona and get caught by say, Blitzcrank, chances are, you're dead.
  

• Protect ADC. They are squishy, but have more damage potential than you do later on. You'd want to take damage for them or help them avoid taking damage. Of course, there will always be a dumbass that takes free damage for no good reason, I suggest bearing with it and telling him not to do so.
  

Reli's 3rd and 4th point important, don't ignore.

EASY SUPPORT TO START WITH

Honestly, not to sure on this. Soraka's the easiest since all she does is heal, heal, heal, but in the current meta of heavy cc, she isn't really that useful with just a silence. I thought of recommending Annie, but she's kinda a one-trick pony as well since her main selling point as a support are "instant" stuns. I guess I'll use Sona as an example here, since playing her teaches proper positioning (so you don't die), her spells are easy to understand and her kit has quite a bit of utility overall. Taric is good to start with as well, but I'm biased to Sona since that's how I started   

Sona
Passive- Every third spell cast gives an additional effect on next autoattack and said autoattack will also do more damage. DOES NOT APPLY TO R
If Q, double damage (of the AA). This is good to poke with.
If W, target's damage output is reduced for 3s
If E, Applies a 2s slow to the target

All of Sona's spells, except R, have a passive aura if it was the last spell cast

Q- On activation- Deals damage to 2 targets in range, prioritizing champions. Your poke skill.
 - Aura- Gives allies (self included) additional AP and AD within a certain range.
 
W- On activation- Heals nearby ally and Sona. Also gives extra MR and Armor for 3s. Prioritizes lowest health percentage ally
 - Aura- Gives allies (self included) bonus Armor and MR

E- On activation- Grants extra movement speed to nearby allies and self for 1.5s
 - Aura- Extra movespeed within certain range for allies and self

R- A 1.5s AoE stun

In lane, you'd want to poke at enemies with Q and autoattacks while making sure you yourself don't get caught. Do not all-in until level 6 (preferably). When engaging as Sona, you'd want your R to hit more than one enemy. You can use Flash to close the gap and hit enemies further away and catch them off guard. Follow engagement up with Qs and AAs. Retreating is the same thing, use R, and spam E and W. Later on when teamfights start to begin, you can still initiate, but you should almost always return to your carry to protect him.

Build wise, usually all supports build the same thing. This consists of items like Mobility or CDR boots, Ruby Sightstone. Items that have CDR/Mana regen are good too like Mikael's Cruscible (Crucible also allows to cleanse CC, very useful). Aura items like Aegis of the Legion also help the team, so get that. The jungler can get Locket too, and the passive doesn't stack, so communicate to see who should build it. Also, since you won't be farming creeps, its nice to get gold generation items like Ancient Coin, Relic Shield and Spellthief's Edge. Usually you'd want the Coin for mana and hp regen AND later on it builds into Talisman of Ascension, which gives speed boost for engagement/ disengagement. This Shield gives more HP regen than Coin, and has a passive which allows you to execute a minion and give hp and bonus gold to a nearby ally. Its final upgrade allows you to give a shield based off you current health that deals damage after 4s. Spellthief's gives AP, mana regen and when you hit an enemy or tower with an autoattack or skill, you get gold. Final upgrade applies a slow.


I think my post is getting a bit lengthy  , I should stop about here. There's probably someone else here that can give better insight than me, so don't take my advice like the word of god.


@Aria congratulations