If I'm correct, today (Monday Sept 8, 2014) It's at Rosedale at 6PM. Do I just show up say "Hi, I'm here to play."? Is there somewhere else that has more detail?
Although I have not been to this league in particular, to answer your question, yes you would just show up and get in the league. All of the leagues you can show up with no warning and play in. It is not like a bowling league where you commit to so many weeks. As long as the league is still going on you can go to one night or 5 or all.
That being said many of the leagues are winding down now. With the fact that there is less and less light out many leagues have to move up their start time to 5:30 or even 5:15.
I know that doesn't fully answer your question but I hope it helps.