Domain means the inputed x values on the x-axis, so to make things simpler and to not write every individual x values. We write it with <, >, and =<. (you can see it as the 'width' of a graph).
Range means the output y values on the y-axis. It's like the 'height' of a graph. And also, to make things simpler and to not write every individual y values. We write it with <, >, and =< with f(x) too because f(x) = y.
