Helping with understand how the ue4 work

I have probably stupid question, but can’t figure it out on my own.
How the ue4 works? Now i try learn from Shooter game example, and in visual we have file like ShooterEngine, shoterGame …
and i really don’t know where to start reading this code
i found some tutorial called ‘Unreal Engine 4’ Network Compendium, and it help a little, but without any example made step by step, still don’t know what to do.

So what is going on whe we launch a game? where evrything start?

right now i understand it like that:

  • in project settings, we set default starter map, and this map should be use to create main menu, with UMG or with class HUD and slate
  • in project settings, also set default game mode, default pawn, playercontroler, game state, player state

when we run our game, ue4 load first deafult map, and default game mode, that contains rules of the game
and this default classes take controll

but on all maps in world setting we can set difrent game mode, like create one game mode for deatch match and one for capture the flag.

am I on good path, or em I iIdiot?
and where start read this shooter game example?