Effect can be a noun or a verb. Affect is a verb. As a result, "effect" is rarely used as a verb. Effect means "a result or an influence," e.g. side effects. Affect means "to influence or make a difference to." Notice that affect needs a subject to function, "to influence or make a difference to (something or someone.)" This is why "affect" is used where you need a verb. You tend to hear affect in natural disaster reports "affected areas." Let' say there is a hurricane. You will have an affected area that suffers from the effects of the hurricane. The effects (noun) of the hurricane will affect (verb) an area. A good example for the difference is medication. Medication may have "adverse effects." Should you suffer from one of these, then you will be "adversely affected" by medication. Again: medication has adverse effects (noun) that may adversely affect (verb) you.

Here's an answer I gave to someone last week: ............. "Affect" is a verb - to affect : "Can you tell me how the new rules will affect us?" It's usually pronounced 'uhfect'. "Effect is a noun - to have an effect : "Can you tell me about the effect of the new rules?" It's usually pronounced 'iffect'. NB There is also a verb "to effect", but it's quite formal, and not used in everyday contexts.

Both of the other answers are correct. "Affect" is usually a transitive verb, meaning it needs an object: "He affected how I thought about the matter." "Effect" is commonly seen as both a verb (as in "to effect a change," that is, to make a change) and a noun ("cause and effect"). However, in rare instances, "affect" can also serve as a noun, usually meaning a feeling or emotion: "She studies the role of affect in politics," meaning she studies how feelings or emotions affect politics. Again, not common outside certain contexts, but still good to know.