This is another pair of words that is confusing to use in the right way. I will try to explain it to you simply.
The word Everyday is an adjective that describes things that are ordinary or commonplace.
example: Suits are my everyday clothes. ( I ordinarily wear suits )
These are my everyday shoes. ( I ordinarily wear these shoes )
Everyday also answers the question "what kind?"
example: Samantha - "What should I wear tomorrow?"
Ben - "Ah, just wear your everyday clothes."
A noun almost always follows Everyday except if the noun has other adjectives describing it.
example: Bentos are my everyday cheap lunches.
The phrase Every day indicates that something happens each day. It also answers the question "when?"
example: I take the train to work every day.
If you can change every day to each day then every day is the right choice.
example: I take the train to work each day.
I hope that helped you understand how to use the two!