If you click on this option, you will see these functions listed. The main source of functions is, not surprisingly, the function key . As you can see, there are many functions available. Covering each one of them would take a very long time indeed, so we won't do that, but we will cover a few to give a feel for how they work. First, a bit of terminology.
Functions have what are called arguments in mathematics.
These arguments are nothing more than the variables you need to plug in to get an answer from the function. As an example, say you are using the PMT function to analyze your options in purchasing a home. These are the arguments for this function, and there appear to be 5 of them, potentially. The insertion mark is in the first field, Rate, and at the bottom you see an explanation of this field. We see that Rate is defined as the interest rate per period for the loan.