You can't use this applet on your calculator, but your calculator does have sine, cosine, and tangent buttons.
Click the "Show Trig Ratios" button and experiment by dragging point A to form different triangles. What do you think the sine of angle [math]\alpha[/math] represents?
What do you think cosine of [math]\alpha[/math] represents?
What do you think tangent of [math]\alpha[/math] represents? (This one is a little tougher; remember that they're called trigonometric [b]ratios[/b].