|I'm not sure what you are asking for.|
If you want to know what functions to use in Excel create random numbers, there are 2 Excel functions (RAND and RANDBETWEN) and well as various VBA methods. That's why I suggested that you review the Help files. Besides describing the functions themselves, the Help files offer some tips on using them.
On the other hand, if you are asking us to breakdown the internal workings of Excel and tell you how the program generates a random number when you use the RAND or RANDBETWEEN functions, then I suggest you Google:
Excel RAND algorithm
I hope that helps.