Explanation:
You need two more pieces of information: either two sides, or a side and an angle.
Given two sides, the third side can be found with Pythagorean theorem, and the angles can be found with trigonometry.
Given an angle and a side, the remaining angle and sides can be found with trigonometry.
To use trigonometry to solve a right triangle, use SOH-CAH-TOA.
Sine = Opposite / Hypotenuse
Cosine = Adjacent / Hypotenuse
Tangent = Opposite / Adjacent