Differences between "Total users", "Users", "New users" and "Returning users"

What's the relationship between "Total users," "Users," "New users," and "Returning users."

1. How do "Total users" and "Users" vary from each other?

2-1. Is the following equation accurate? (# of total users) = (# of new users) + (# of returning users)
2-2. If 2-1 holds true, where can I find the count of "Total users" in a GA4 report?