[Help] What does the code do?

Hello. So today I am starting out with UE4, however, I found a problem.

After I made a class for my player, it was preloaded with a shitton of code I do not understand.

I am experienced with Java and somewhat with C#, so I expected it to be easy to jump in from an extent… but, this doesnt make sense at all! So, can someone explain what the code does, where I should put my functions, and how to edit it? Thanks in advance.

Specifically the First Person Shooter character class