Help with private student loan terms

I have found all kinds of calculators that can do this work for me to calculate student loans, but I am curious about the actual formulas that it takes to get these answers. Most private loans are variable rate, but I am trying to find something that will help me figure things out as close as possible.

• What is the value of the loan after the deferment process when payments begin if interest is compounded monthly?

• How much will my monthly payments be?

• How much interest will be paid by the end of the loan?

I'm not sure if this is enough information, this process is so confusing.