(YouTube video created by Arkady Etkin.) (GIF created and contributed to Wikimedia Commons by Tdadamemd.)
You should also play around with the nifty Desmos creations through the links below:
Unit Circle Showing Sine Graph and Unit Circle Showing Cosine Graph.
Unit Circle Showing Sine Graph and Unit Circle Showing Cosine Graph.
When you are ready, move on to the coordinates page to understand the final component of the Unit Circle.