The screen is designed to help you solve trigonometric equations.
The general equation is : A sin(Bx + C) + D = E, or the equivalent with cos and tan.
You change the values of A, B, C and D using the buttons at the bottom of the screen.
You can change the value of E using the slider, which also draws a horizontal line on the screen.

The number of solutions for each equations depends on the inverval chosen. There are several possible intervals available in the drop down menu at the top of the screen.
The number of solutions and their values are displayed on the screen. The values have been rounded to the nearest degree.
Play around. I hope you will find this applet helpful.