Money system... Need all the help and ideas PLEASE... thank you

I’d like to make a game that contains a “Money” system, im newish to java code and only know basics.
so id like to know where to start and what i should know in order to get started. can anyone help?
for example:
Fpscharactor walks over money found laying on floor.
how would it get added to their Money “amount on hand”
Please help thank you

This might help you:)