Add the suffix -er to the end of a base word to show comparison between two things. Add the suffix -est to the end of a base word to show comparison among three or more things. Use the basic rules to spell words correctly when adding suffixes -er and -est. 1. click 2. use the tool and add an -er and -est to the words. 3. use the and read each word 4. click on the green to submit your work.