Hello!! Thanks for the feedback!!
Aphelios has a lot of combos because he is a champion where the sky is the limit. You can use everything with everything and make it work in the proper situation. But here are some common ones that you want to try:

- Crescendum, the Chakram with Severum, the Scythe Pistol or with Infernum, the Flamethrower, you use Q with pistol or flamethrower and gain chakram stacks. Then switch to Chakram and start auto attacking enemies to preserve the stacks. And when they are about to expire switch again, use Q, and switch back to Chakram. It is the highest DPS weapon with auto attacks if you manage to get the stacks.
- Crescendum, the Chakram with Calibrum, the Sniper Rifle, the Q can place turrets to mark enemies and poke them from very far. Also in teamfights you can Q with chakram to place turret, switch to sniper, and q,r get a ton of chakram stacks switch to chakram again and deal lots of damage with every auto attack.
- Gravitum, the Gravity Cannon you can 5 man R and snare them with Q. Great potential for wombo combo.
- Calibrum, the Sniper Rifle with Gravitum, the Gravity Cannon, you Q with calibrum and auto attack for the mark while cannon is on your off-hand. Then switch to cannon and Q. Thus you can snare the enemies from a very long range.
- Infernum, the Flamethrower with Gravitum, the Gravity Cannon, if the enemy are grouped up you can Q with flamethrower, slow them, and then Q with cannon for multiple snares.

About the runes, of all the keystones, the best 2 are Conqueror and Lethal Tempo. The choice is affected by the playstyle of each idividual and thus the option is in most cases a personal preference. That is the case because, Conqueror offers good amounts of AD and healing, keeping you healthy while in the same time dealing lots of damage and is more like focused on flamethrower, cannon and sniper without implying that is bad for the rest of the weapons. Lethal Tempo on the other hand offers very high attack speed which synergises perfectly with chakram because you get stacks very fast and chunk enemies with every auto attack. Press the Attack could be an option for trades in laning phase but it is very weak in the late game where Aphelios trives and for that it gets out of the competition. It is just bad. You are a late game champion and investing in early is like trolling.

I hope i covered you! If not feel free to contact me again!!