I don't understand how to implement this gun with C++

Hello. I am very new to unreal and i want to implement a feature, but i’m afraid it’s more than my knowledge in C++ permits.

I found a tutorial that is as step by step as it can get but i have trouble understanding what to copy paste and where! I’m very rusty at programming lines. I created a character and actor class but don’t understand the method to link them to blueprints of actor and gun BP in unreal.

Here’s the tutorial : Recreating the Gloo Cannon from Prey in Unreal (C++)-Vitor Cantão

Here’s a preview of the scene i will add it to : 9 WIP_Lobby - YouTube

He will meddle with the character’s ability, projectile and gun pickup. How do these classes fit with existing entities? Is someone able to give a more step by step maybe a video walktrough of the first part?