No Problem in asking at all , the connection is as in the diagram with numbers connected to arduino , also in the code the library used is defined a pins connection of arduino , you are welcome at any time and be free to ask :)

This code works with arduino uno , so please make sure use it , if you want to make it work with any arduino on any battery you will have to use analog input and voltage devider based on your battery , then change the function that read from the internal voltage level to read from the analog pin , and lastely you will have to change the voltages values in if conditions to suite your battery level and you visual need.

it is ok , we have that novice time at a point , and yes you can add it to existing project, simple copy all the codes in the project and add it to the other project , but combine the process in the setup function with the new function , and the do the same for the loop function , if you wish to make it with timing you can add the TimerOne.h library and set the function in the loop to the function that will work with timerone function and remove it from the loop function.