If you're setting up a Group Ride or Race on Zwift, you want to be sure you advertise that on the TeamUp calendar.
There are specific instructions on how to set up Races or Rides so others can find them, synchronize and attend your event on-time and with the correct rules followed.
See the following article describing how to add your event to the calendar that others use to find their rides:
Skye Nott has written a really great article over on Staminist on setting up a Group Ride on Zwift. The article allows commenting, so leave your input or questions if you want to contribute to the discussion.
Eric Schlange has also written a very detailed blog post specific to Race events on his Zwift blog:
The above articles should provide you with all the details you need on joining a Group Ride or Race as a participant, or setting one up as a ride leader.
Have fun on your ride!