These words give writers trouble since the two can be both a noun and a verb, although affect is typically verb and effect, noun. Normally, you will use affect to denote influence. For example:
If I play music will it affect your studying?
Affect used as a noun means “emotion.”
On the other hand, effect, which is more commonly used as a noun, relates to the consequence or result.
The effects of the drug have long since worn off.
As a verb, it means to cause or to accomplish:
The tornado effected a change in our plan.
Another couple of closely related words which mean different things are accept and except. Accept will refer to receiving or approval of something.
I accept your apology.
Except refers to an exclusion, as in, not including.
I took all those classes except math.
Because they sound so similar, these words often become interchanged when we write but meaning two different things, they can really botch a sentence’s meaning!