Each is used with countable nouns in the singular. Each can also be used without a noun. Every is used when we talk about people or things as a group. Every is also used with countable nouns in the singular. Each department has its own secretary.
Every member receives a copy of the society's journal.
Put when , if , so , such , each , every into these sentences. I'll be at the office day next week. I think I'll go to bed. I'm not sure I'll see James tomorrow. I don't know whether he's coming to my meeting.