suffixes

particles or suffixes are added to the final syllables that a word usually a verb to form a new one.many occupations and professions are formed by adding the suffix
ER to the base form of the verb.example:
teach-teachSing-Sing


if the verb ends in a vowel and a consonant then double the last letter and add suffix ER



run-runner
program-programmer


if the verb ends in E we add R:


drive-driver
write-writer

http://www.youtube.com/watch?v=4Zk4MnMJ-vE