Two rays with a common endpoint form an angle, with the vertex being their point of intersection. Angles are measured in degrees using a protractor, from 0 to 180 degrees. There are four main types of angles: right angles measuring 90 degrees and forming a square; acute angles between 0 and 90 degrees; obtuse angles between 90 and 180 degrees; and straight angles measuring 180 degrees and forming a straight line.