Culture has to do with practices, lifestyle, the things that are considered everyday. It's the "normal" for character. Do they eat big meals or small? When do they eat their biggest meal? Is it normal for a family to sit together to eat. Is "family" a normal thing at all? What religious or spiritual activities does the character engage in? Is it normal for people to have jobs? Do they barter or use currency? What kind of currency? Etc. Etc.

If your story is set in a real, current setting with which you're familiar, you may not need to spell it out. If your story is fantasy, you may need to fabricate the details. If your story is historical fiction or takes place geographically someplace with which you have limited familiarity, you may need to do some research.

Cheers,
Michelle