WEEKDAY vs. WORKDAY explained
Imagine you've got a dentist appointment on October 15, 2018. You typically work Mondays, Wednesdays, and Fridays, so you'll need to know if you should request off work for this appointment.
Using a calendar, we'd go back to the given date and determine that it's on a Monday, so we'd need to request off work.
The WEEKDAY function does the exact same thing!
Given a date, the WEEKDAY function returns a number between 1-7 representing what day of the week the date is on.
The WORKDAY function, by contrast, is completely different. It's easy to get them twisted though, so let's visualize the difference.