Question

what are the functions how can you use any of them

Answer 1

Functions are the pre defined formulas in Excel.
We can use them to have addition, subtraction, multiplication, for having averages of the set of data and lots more.

For beginning a function you shall neeed to have formula as wel as you must be known about the data range.

Answer 2

We can explain functions by simple example
If we take a dog we will will see that it will have some characteristics and some functions
It's functions will be barking walking etc
This is for understanding functions
If we have to define function then we can say that the functions are the data members of objects