The return keyword is used to exit from a function or to return a value from a function (and exit it).

function isAdult (age : Int) : Bool
{
   if(age < 18)
   {
      return false;
   }
   return true;
}

This is a function that should help you understand how to use the return keyword. It returns false if the age is inferior to 18, or else it returns true.