If you search for the words affect and effect on the web, you’ll find, generally speaking, that the advice to help you differentiate between the two words is to remember that the one beginning with ‘a’ is a verb that means to make a difference to and the one beginning with an ‘e’ is a noun that means the change that results. My teachers told me much the same thing.
So, I might say that this knowledge has affected my ability to distinguish between the two words so I don’t suffer the embarrassing effects of a mistake.
But, the word effect can also be a verb. The Oxford Dictionaries online gives the meaning as ‘to cause (something) to happen’ or ‘to bring about’. So, for example, I might say I have effected a new plan for 2012.
See the usage note here for more.