How do I use ROW_NUMBER()?

Question

I want to use the ROW_NUMBER() to get...

1. To get the max(ROW_NUMBER()) --> Or i guess this would also be the count of all rows

Answer 1

SELECT num, UserName FROM 
 (SELECT UserName, ROW_NUMBER() OVER(ORDER BY UserId) AS num
  From Users) AS numbered
WHERE UserName='Joe'