Mid()

=mid(text,start no,num char)

This formula is like left and right formula
but it pick the no. of digits you define from/after the digit number you tell.

Text= Cell number
Start no= From left from which digit you what to start.
num cha= Number of Characters from the start no.

Networkdays()

=Networkdays(Start date,End date,Number of holidays in a week)

This Formula will help to get number of working days for a defined period.