The words "effect" and "affect" are commonly misused in the English language. Affect is usually used as a verb, and effect as a noun. The easiest way to remember the difference is to think of "affect" as something that happens to someone or something. An effect is an end result.
Ask yourself what you are trying to say. If you are trying to say that something was caused as a result of some action, use "effect." For example, the sentence "The drug had an immediate effect on the pain" is a correct use of "effect." To use "affect," write "The drug immediately affected the pain."
Ask yourself if the sentence shows that a person was moved or persuaded by something. "The snow affected John's sinuses" says that the snow had an action on John. To use "effect" correctly, write, "John didn't like the effect of the snow on his sinuses."
Use "affect" as a noun if you are writing about psychology. According to Grammar Girl, psychologists prefer that because you can't truly know what someone is feeling, so can only quantify what you see or are told. So treatment may have a happy affect on the subject.
Use "effect" as a verb if it means to create or accomplish something. So, you would write "Gina hoped to effect momentum with her ace block," to say that she wanted to create momentum.