This is an especially confusing pair.
affect is usually a verb: Raising interest rates will affect how many people borrow money.
effect is usually a noun: The effect of raising interest rates is that fewer people borrow money.

However, there is a noun “affect” (pronounced with the emphasis on the second syllable instead of the first, AF-fect) which is used in psychology to mean “the ability to feel things”: He suffered from flat affect.

And there is a verb “effect” meaning “to bring about”, usually applied to change: The new government plans to effect an immediate change in interest rates.

The safest thing with this pair is to check every time.