In the first window, use the mouse to sketch a signal x(t), or select one of the provided signals. In the second window, clicking on the t axis will set a value of T, and x(T-t) will be displayed as a function of t.
If you click to set T at zero, the flipped signal x(-t) is shown. The value of T can be dragged with the mouse to show how the flipped signal is shifted for different values of T.