Well, Aphelios Early Game is horrible, he doesn't have damage to fight with some ads, and he don't have an escape ability to avoid an level 2 Engage from Tanks Supports (Like Alistar, Leona or Rell), so you should just focus on farm, and even poking a little your enemy with you green weapon(Calibrum), and if you get poked too much just heal yourself with the red one(Severum).

At Level 1 you gonna have Green-Red, and you can think that you gonna use the green one because of the long range, but no, you gonna start using the red one, when you come to the last 10 bullets of the Red one, you gonna have the chance to do your first combo, you gonna use the Q of the Red one, marking the target with the passive of the Green one, after that the Red will become the Purple and you gonna use the Q of the Purple, snaring the target, and you gonna trade your guns( W ), and gonna use the Q of the Green one at the snared target.

RED Q (Red -> Purple) - GREEN PASSIVE AA - PURPLE Q - GREEN Q

You need to have Blue-White, and the Blue 10 bullets or less, you gonna use Q of the Blue one on the minion wave, stacking chakrams, then the Blue gonna become the Red and you gonna use the Q of the Red, stacking more chakrams, and then you just trade the gun for the White one and just AA them.

BLUE Q (Blue -> Red) - STACK CHAKRAM FROM WHITE PASSIVE - RED Q - STACK MORE CHAKRAM FROM WHITE PASSIVE - W - AA WITH THE NUMBER OF CHAKRAM THAT YOU STACKED

I'm a 15 years old LoL player, without rank, that like to learn about the champions that I like, i dunno if this guide gonna be usefull to someone, but I wanted to do this, thank you :)
Obs¹: I'm a brazillian, my english is not perfect, so sorry
Obs²: Credits: https://www.youtube.com/watch?v=ZDI9VUmip68 / This is a guide made by a brazillian coach with a mono Aphelios of the BR region, and almost everything that I learnd was from there
Obs³: I really don't know anything about Synergies and Threats, so I won't try putting things that I am not sure about