With this build, you are meant to be a very supportive character.
When your build is complete you will grant Movement Speed, Attack Damage, Lifesteal, Magic Resistance and Health Regeneration to your allies just by being there, plus an attack speed bonus if you heal them.

This is an AOE ability thas slows the enemy and heals you. You can use it to poke the enemy and restore your health after healing an ally. The more enemies affected by Starcall,the more health you gain back. Try to predict where the enemy is going to stand. It's easy when Draven uses his Spinning Axe or when Bard places his Caretaker's Shrine

Ths is your base spell. Heal your ADC every time you can.

This ability silences the enemy and can root them. Usually I use Starcall and Equinox together to ensure to root them. If the enemy is using Teleport land this ability on the turret/minion/ward to instantly root them when they arrive. Also works against Stand United, Destiny and Hyper-Kinetic Position Reverser.
The same thing happens when the enemy uses Zhonya's Hourglass, Guardian Angel and Tempered Fate.
If you are dealing with an invisible melee character like Shaco or a blinking melee character like Katarina, stay inside Equinox to protect yourself (allies should stay inside too).

This is a game-changing ultimate. You can help allies in other lanes with this. If you are running with Salvation towards an ally in danger, but you think you're not going to make it, use Wish and then spam your ally with Astral Infusion.

Artic Embrace shoots an ice lance that slows the enemy by 80% for 2 seconds. Use it among with Starcall and Equinox.

The active shields you and nearby allies. Use on teamfights.

Salvation can be a very useful passive when running to heal an ally. Use it to help your jungler while you're on lane. Sometimes it can help you escape.

This passive gives you the ability to grant 25% extra attack speed for 6 seconds to the allies you heal.

When you are out of combat, you gain a lot of movement speed. It makes saving allies easier. It gives you massive speed with Salvation.

Giving your allies 10% extra movement speed is always handy.

Zeke's Herald You give extra damage and lifesteal to nearby allies. It works better if your ADC has Bloodthirster or Essence Reaver.

Giving extra magic resistance and health regeneration is very handy.

Spell Vamp is very good with Starcall.

At level 1, try to poke the enemy with basic attack and earn gold with your Spellthief's Edge passive. Try not to heal the adc so much, because you can't regain that health. At level 2 you can heal yourself with Starcall and poke the enemy with it, but always remember the basics for the gold. When you reach level 3 you should hide in a bush and use Starcall and Equinox together. Never use your Equinox alone because it has way too much cooldown and mana cost.
When you reach level 6, keep an eye on your allies health bar, your ultimate can save them from fatal blows. When you are going back to base, heal your allies all you can with Astral Infusionif there aren't dangerous enemies arround or a Jinx, Ezreal, Ashe or Draven on the enemy team, because they can use their ultimate.