Affect? Effect.

This mistake is so common. I'd be a rich, rich girl if I had a dime for every time I saw this error.
In simplest terms: Affect is a verb and effect is a noun.

One word is used to show action, and the other one is a person, place or thing.

So you would never say this:
How does that effect the final product?  In this sentence, effect is clearly used as a verb, which doesn't work because affect is a verb, not effect.

Instead it would be:
How does that affect the final product?

Effect is used as so:
The effect of not studying for the exam is possible failure.  In this sentence, effect is used as a noun.