The given angle within the circle can be changed by moving the α' slider at the top (-2880 through 2880). Check boxes will display different content, it is advisable to limit your check to at most 2 or 3 at a time. Follow the instructions below initially.
All coterminal angles are an angles of different measure that share the same initial side and terminal side.
A reference angle is the acute angle formed by the terminal side and the x-axis. (The only values a calculator recalls are the reference angles.)
SohCahToa is a mnemonic device to assist in remembering the sine, cosine, and tangent ratios. (Memory Trigger)
The vectors of the sine and cosine are a visual representation of the values of the sine and cosine functions.

1) Move slider left and right to observe the line that move and the x- and y-values on the point on the end
2) Check the Vectors box to observe the values and segment lengths that are displayed {un-check box}
3) Check the Positive Coterminal box; this displays the positive coterminal angle between 0° and 360° for the α' angle {un-check box}
4) Check the Negative Coterminal box; this displays the negative coterminal angle between -360° and 0° for the α' angle {un-check box}
5) Check the Reference Angle box; this will display the reference angle for any given angle {un-check box}
6) Checking the Functions box reveals the mneumonic SohCahToa check box; checking SohCahToa allows the user to compare the coordinates on the circle to the value of the sine, cosine, and tangent functions.
7) When you are ready to view the reciprocal trigonometric functions, click the check box
8) Be sure to notice when a function is undefine. Can you explain why?
While working with the trigonometric functions, the Vectors and Reference Angle check boxes assist examinations of the functions.
Additional Resources include: http://en.wikipedia.org/wiki/Angle