In a rightangled triangle, for any not-right angle alpha those formulas hold:
sine of alpha = opposite leg / hypotenuse
cosine of alpha = adjacent leg / hypotenuse
tangent of alpha = opposite leg / adjacent leg
In those formulas, the opposite leg is opposite of alpha, the hypotenuse opposite of the right angle and the remaining side is the adjacent leg.
There are also formulas that consist of sine and cosine and make calculations in arbitrary triangles possible.
Trigonometry
Mathepower can do trigonometry calculations step by step in a right-angled triangle.