After launching your VM, navigate to http://your_vm_public_ipv4 in your browser where you will be prompted to create the first user. This account will have administrative privileges.
When you first login, go to Settings->Admin to upgrade to the latest version of Saltcorn.
If you would like to connect using encrypted HTTPS traffic, the simplest is currently to use a load balancer and install a LetsEncrypt certificate.
To run the multitenant instance, you will have to SSH into your VM and edit the file /home/saltcorn/.config/.saltcorn as described in the Multitenancy wiki page.