What is the relationship between two perpendicular lines? What are some examples?

All four angles formed by two perpendicular lines are measured ${90}^{o}$.
The definition requires only one angle (out of four formed by two intersecting lines) to be the right angle (that is, measure at ${90}^{o}$). Obviously, all others are also measure ${90}^{o}$ since an angle adjacent to one measured ${90}^{o}$ must complement it to a straight angle of ${180}^{o}$ and, hence, must be ${90}^{o}$ itself.