How would I connect the thunderbolt 3 Macbook pro with a Thunderbolt 2 monitor?
You could use something like the also newly-launched Apple Thunderbolt 3 USB-C to Thunderbolt 2 adapter. Apple's 12" MacBook has a USB-C port but does not integrate Thunderbolt into it, so Apple did not make a product which needed a Thunderbolt 3 to 2 adapter until now.