As support it is your job to help the team. In laning phase you need to keep vision and set up kills for the adc. Once grouped up with the team you need to stay near the front and try to catch the enemy out and keep the enemies off your adc and mid laner.
Runes & Masteries
You mostly want to have defensive runes since you will be defending your team. There is times where you want some damage so you can help your adc harass the enemy adc in lane. For masteries if you are taking the damage route go thunderlords and if you are going to heal and protect you want to take Windspeaker's blessing.