maybe I am too late, but perhaps this will help you in the future;
With Tmin and Tmax you set the limits of the domain of your parametric function. That means if you choose for a smaller Tmax you only get a part of the function's graph. For instance: Set Tmax=1 and look what will happen to your graph.
The most important value is tstep. The smaller tstep is the more exact the graph of the function is drawn, but the more time it takes to calculate the table and to draw the graph. For instance set tstep = .01 and watch the procedure of drawing.
With xmin, xmax, ymin and ymax you construct the frame around the picture which contains the graph of the function. For instance: Set xmin=-10, xmax=10, ymin=-10 and ymax=10. You'll get the same picture but very small because you have enlarged the frame by the factor 5.
So it is necessary to get a little bit experience to set the frame accurately. There is no connection between the domain of a function and the size of the window which shows the graph but one: It would be very convenient if you can see the most important parts of the graph.
One last remark: As you may know you find the table containing t, x(t) and y(t) under yellow+F5.