You see, from left-to-right:
- User info (avatar, name + link, badge count, how long ago they joined)
- The ranking in this league. For the monthly league, ranked by how much reputation you gained in the current calendar month, but there is also a weekly league (current week starting on sundays), and quarterly, yearly and overall leagues. It's the place the user ended up at when the table was sorted on the last column.
- Change from the previous ranking for this league. A positive number means the user rose in rank, negative means you dropped.
- The total amount of reputation the user had at the time the rankings were calculated. (This can be lower than the last column; you can have lost reputation to bounties and such).
- The reputation change this week / month / quarter / year, or for the total rep league, the total reputation, at the time the league table was generated.
So, for your specific example: you are ranked 416th, you gained 17329 places compared to the previous month, were you were ranked 416 + 17329 = 17745th.
You can visit previous rankings with the links at the top, but there is no graph charting rank placings; these tend to jump around a lot for most people. For Jon Skeet, it'd be a rather monotonous almost-straight line.
Most sites include a 'top [percentage] this [league]' on the user summary page by the recent reputation changes table. When visiting the "Users" tab, there is a link at the bottom of the pages to the leagues. You'll also find a tab on https://stackexchange.com/ ("Top Users").