Well, I dont know mac. But you can go too options > Plugins > install plugin and select the plugin
Or drag and drop it into rhino. Then commands should be usable. On windows at least
do you have sketchup pro? if so, you could try using .3ds exports from rhino then import that into sketchup… .3ds has a few limitations (such as polycount per group is ~65k) but it’s the fastest format for getting things into sketchup from rhino.
if you don’t have sketchup pro, you can try one of the OBJ importer plugins for sketchup like this one:
it’s possible we’ll see a Collada exporter (.dae) in mac rhino soon in which case, that will probably be the best way to go between rhino and the free (and pro) version of sketchup