If you're scheduled to meet with your provider on Doxy.me, he/she should have given you a unique link to their Doxy.me room. It looks something like:
Review your appointment reminder or calendar invite for your provider's Doxy.me URL. Once found, click the link to check in to their room.
If you still can't find your provider's Doxy.me room link, contact your provider and ask them for it.