Differences between "every day" and "everyday"

In short, "everyday" is an adjective that describes something ordinary or commonplace, while the phrase "every day" means "each day."

every day      부사구      "매일"
everyday       형용사      "매일의, 일상의"


examples)

I'm most comfortable in my everyday clothes.

나는 평상복을 입을 때가 가장 편하다.

I take a shower every day.

나는 매일 샤워를 한다.

refer to : http://www.wisegeek.org/what-is-the-difference-between-everyday-and-every-day.htm