There are four main types of angles: straight, right, acute, and obtuse. Two angles are congruent if they have the same measure. Adjacent angles share a vertex and ray. Vertically opposite angles formed by intersecting lines are congruent. Complementary angles add up to 90 degrees. Supplementary angles add up to 180 degrees and form a straight angle. When a line intersects two or more lines, it forms pairs of angles. Corresponding angles, alternate interior angles, and alternate exterior angles in the pairs are congruent.