Here's a rundown of Olorun's abilities.
Passive: Touch of fate
Once at 150 Magical Power from items, Olorun gains 15% Critical Hit Chance and a further 1% per 10 Magical Power from items. Olorun’s critical hits only deal 50% increased damage.(rather than 100% like normal crits) Additionally Olorun gains 5% extra scaling on his basic attacks.(this caps at 70% crit chance) Reaching the crit cap is why so much high power is rushed in this build.
1: Focused Light
Olorun charges an orb of pure energy for up to 2s before firing it in front of him. The longer he charges, the farther the projectile goes, passing through and damaging enemy minions, but stopping on the first enemy God hit. This ability can Critically Hit and can provide stacks of Overflowing Divinity. This ability is your best wave clear, and your main big damage spell. Note that charging the ability longer does not change its damage, so if you can hit your target at close range, fire it immediately. It also travels significantly further when using it in Olorun's Sanctified Field, which can help secure kills on escaping enemies. (try to poke enemy Gods with it while also hitting full minion waves, so you can stack Overflowing Divinity)
2: Overflowing Divinity
Olorun gains amplified Attack Speed. Every successful attack on an Enemy during the buff provides his inner Sun with energy, to a cap of 20 stacks. During the buff or for 4s after, Olorun can refire this ability to conjure the Sun to damage Enemies in an area. The Sun emits projectiles faster and more randomly with higher ammo. Hitting the same Enemy deals 10% less damage each time, to a minimum of 80% reduction. Due to how unlikely it is for an enemy to stay in the sun projectiles for the full duration, don't worry too much about firing it at full stacks(if you can, great, but fire it at low stacks too for bits of damage) And if you are being hounded by a melee enemy, try placing the Sun target at your feet to either deter or at least heavily damage your attacker if they stay on you.
3: Consecration
Olorun expends the light within himself knocking back and damaging nearby Enemies as well as slowing them for 2s. Allies bathed in the light gain a heal over time that ticks every second for 5s. For every ally healed, Olorun gains Physical and Magical protections. If you're being poked out of lane a ton, or if you're consistently healing allies, consider leveling this ability quicker than Overflowing Divinity. The protection buff from this ability is quite high at 80 protections if you heal 5 teammates, so consider nestling into your team to heal and get the buff, if you feel like you're in danger of being targeted.
4: Sanctified Field
Olorun creates a large area of divine energy that distorts the flow of time within. All Enemies caught in the area are negatively affected by the time dilation, attacking, casting and even animating more slowly.(40% slower) Olorun himself benefits from the Sanctified Field in a similar way.(30% faster) The strength of the divine field also impacts the effect of buffs, debuffs, projectiles and deployables.
It's quite hard to detail what to do with this ability as it has so many interactions, for enemies, if they use items like aegis, or abilities that protect them, it'll actually prolong those defensive effects, whereas for you your defensive spells like aegis will be worse in the field as they'll go away quicker. The most important facts for it are, position it where enemies can't simply fight outside of it, and make sure that if you're trying to stay in it, you watch for enemy abilities that won't slow down, like a Zeus ult raining on your time dilation parade, forcing you to flee your own field.