The UC calculation is similar to the CSU calculation, except that 12th grade course grades (if available) are not included. The CSU web page explains the calculation more clearly: CSUMentor - Plan for College - High School Students - GPA Calculator
Since you count grades by semester for the UC or CSU calculation, you get one bonus point for each semester of honors or AP course taken with a C or higher grade, up to a maximum of eight such bonus points. E.g. you took two year long (two semesters each) honors or AP courses and got C or higher grades in each semester in each course. You therefore get four bonus points from these courses for your UC or CSU calculation of your GPA.