I'm assuming it's weekends since premiere. Weekend 1 would be the weekend it comes out, weekend 2 would be the following weekend, etc. The left column is just measuring week by week and not all of the movies came out at the same time.
Why is the left and right number sometimes the same and sometimes not?
If a movie is on weekend 1 then the total is just whatever it has earned in this first weekend, so they'd match. Movies that have been out longer will have higher totals than the week being measured.
What is "WW"?
Worldwide, I'm assuming. So the top number would be domestic total and the bottom number would be domestic+international.