If you’ve received a Skype for Business meeting invitation and do not have the Skype for Business application or an account, you can still join the meeting using the Skype for Business Web App!
Join a meeting using Skype for Business Web App
Trouble installing the Skype for Business Web App plug-in?
Set default video device in Skype Meetings App
Set default audio device in Skype Meetings App
Skype for Business Web App help