Find the month at the top and the day number on the left. Where they cross is the weekday.
Find the 13th and look over to Friday. Look up to see when Friday the 13th happens this year.
Please see a much prettier version at time.is site.
To change the year:
Use left-arrow or tap the number side to go back a year
Use right-arrow or tap the word side to go forward a year
Append ?year=YYYY, ?YYYY, ?date=YYYY-MM-DD, or ?YYYY-MM-DD to the url