Collaboration support isn’t in the nightly binary, so you either have to build it and turn that option on or you can download a prebuilt binary from here https://data.kitware.com/#item/602fee7f2fa25629b98dbb7e
With that binary you can do the following to test collaboration (with a buddy as you want more than one person to collaborate 
- Unzip the binary
- make sure your vr headset works with steamvr
- start steamvr
- run the PV binary
- load the state file included vrdemo3.pvsm
- set your Name in the collboration section to your name (what you want your avatar to be labeled as)
- name your session (e.g. ken-test etc) each session is independent
- make sure your buddy uses the same session name
- don’t be inside a really restrictive firewall that blocks port 5555
- hit “Send to OpenVR”
- hit “Connect”
- put on your headset
- make sure your buddy does all this
At that point you should both be in VR in a collaborative session. (and you can have more than two, there is no hard limit)
The left trigger will cycle through saved viewpoints bringing all collaborators together. Tons of other options etc but that is the basics.