The two words sounds similar, but are often used incorrectly. The simple way to choose which to use is to remember one is a verb and one is a noun.
Affect is a verb and is used in sentences such as, “Alcohol affects your ability to drive.” or “The music affected him greatly.”
Effect is a noun. It is usually used with the verb ‘have’. It is used in sentences such as, “The medicine may have some negative effects.” or ”The movie had some great special effects!”