Also you will see a red crosshair on the graph on the left side. This is the initial point; you set the location of this point by clicking the mouse.
You can change the equation by selecting a different left hand side or right hand side using the popup menus.
Underneath the popup menus are a variety of parameters which you can change by clicking on them and dragging to the left or right. Also you can click on the sign to flip it from plus to minus or minus to plus. Double-clicking on the sign will set the value to zero.
Zip archive of this applet.
Another differential equation applet.