Everyday (one word) is an adjective meaning ordinary.

     Example: These are my everyday clothes.

Every day (two words) uses the adjective every to modify the noun day.

     Example: I wear clothes every day.

Here’s a quick tip to help: If you’re not sure which to use, replace everyday/every day with each day. If the sentence still makes sense with each day in its place, then you want to use the two-word (every day) form.