Affect vs Effect
Affectverb
have an effect upon
Effectnoun
a phenomenon that follows and is caused by some previous phenomenon
The difference
Affect is almost always the verb — to influence something. Effect is almost always the noun — the result of that influence. The rain affected the crop; the effect was a poor harvest.
How to keep them apart
Affect is the Action; Effect is the End result. The exceptions are real but rare: effect as a verb means to bring about, and affect as a noun is a psychology term for observable emotion.