The tool used to find the angles in a triangle is called a protractor. Protractors are semicircular or circular instruments that facilitate the measurement of angles in degrees. When measuring the angles within a triangle, one places the center point of the protractor at the triangle's vertex, aligning one side of the angle with the protractor's baseline. The measurement can then be read from the curved edge of the protractor. Knowing the angles in a triangle is essential in geometry, aiding in understanding various properties and relationships within triangles, such as the sum of angles always equating to 180 degrees.