a step function (also known as the greatest integer function) is a function in which any value, be it an integer or something in between, moves to the greatest integer NOT GREATER than the value itself, i.e. if you have 1.9, it would move to 1, if you have -1.3, it would move to -2. So, in your equation, f(x)=[[x+3]] it is going to look like a stairway with each x value corresponding to an integer of y, and your steps are going to be moved up by 3. So the domain will be all real numbers, and the range will be all real integers.