Both words, effect and affect, can be used as a verb and as a noun. But if you found this page through a search engine, it is almost certain that if you want to use a noun, it will be “effect”, e.g.
- It has a negligible effect on me.
And if you want to use a verb, use “affect”:
- It affected me negatively.
Used as a verb, “to effect something” means “to make real, to put into practice”. For example, you can say “to effect political changes” – but this meaning of “effect” is rarely used. “An affect” (which is pronounced /ˈæfɛkt/ as a noun) in psychology refers to an individual’s subjective feelings, but you don’t see it in everyday speech.