Each Servd project allows you to run a single Craft 'codebase' on the platform. This codebase can be a basic Craft site, or it can be a Craft multi-site.
There's nothing special needed to get a multi-site up and running on Servd, but if your Craft `site`s are set up to respond to different base domains, you will need to set up primary domains to cover them in the Domains page of your project.
Once all of your domains have been added to Servd and you have configured the DNS for each of them appropriately, you will be able to visit your project on Servd using each of them and Craft should differentiate between your different `site`s automatically.