To host a Bestiary server yourself, you'll use a MongoDB database. You can host the database yourself, or use MongoDB Atlas. The exact hosting steps are best left to MongoDB's website.

Once you have a database up and running, you'll need two things: the server connection URL, and connection credentials.

When running Bestiary, you can open the options menu via File -> Options (Ctrl+O). In the options menu, enter your server URL, username, and password, then click Save. You'll need to make sure the credentials you connect with have read/write access to your database.