There are no stop signs in Amsterdam and not too many traffic lights. So every non-signalized intersection is more or less a four-way yield. In most cases there is somewhat of a priority direction, but in reality most intersections are just treated as a yield for everyone, meaning most people roll through intersections from every direction. This includes bikes, cars, and pedestrians. It looks a little chaotic - especially to our very regulated environments in the U.S. - but the group is preferring to characterize things as a dance. There is a transportation dance that happens when anyone can go anywhere when it is clear to do so, and not surprisingly, people don't tend to crash into each other. It's kind of like a dance floor that may be crowded with people moving in all directions, but rarely do people actually bump into one another. The video above is a short demo of this dance.
It's quite liberating to not deal with a helmet (very little helmet use, but much better safety statistics) or a lock, and to have a step through frame that is easy to get on and off the bike.
For overnight locking, most people have a heavy chain that they tether their bike to a permanent object - bike racks, street poles, basement window grates, etc. There is a big bike theft problem, but apparently a good chunk of thefts are overnight with untethered bikes. The picture on the right shows my bike locked overnight to a bike rack - the heavy chain connects the frame and front tire to the bike rack and the rear tire clamp is engaged (it is the black circular thing going through the back tire just behind the seat). Also notice the bike rack design - there are two elevations for front tires - this is to accommodate the density of bikes as well as the upright handlebars, which make it difficult for bikes to be parked next to each other at the same elevation and in a way that one can get their bike out easily (see leaning bikes above).
Today the group has some free time to meander around town, get lost, get found, get lost again, and hopefully by 5:15 find themselves at the Anne Frank House for a group tour.