how do you find the angles of triangles with just the sides?

Just adding on to what Melody said earlier:)

Use the Law of Cosines if you have the three sides of a triangle and no angles.

For any triangle with 3 sides a, b, and c opposite angles A, B, and C:

This page explains different ways to use this law:

http://www.mathsisfun.com/algebra/trig-cosine-law.html

You use trigonometry.

If there is a right angle it is very simple trig. (Use 'inverse trig' which is 'arc trig' here)

If there is not right angle then you have to use the cosine rule.