Once OpenStack has been deployed you can interact with your cloud via the CLI by using the standard openstack client commands. The CLI client is provided as part of the openstack snap.
The client recognises the environment variables stored in generated credential files, typically demo-openrc for an unprivileged user, and admin-openrc for the admin user. Source a file before using the client. For example, to use the client as the regular demo user:
source demo-openrc
The following should then work:
openstack flavor list
For help with command syntax see the documentation for the python-openstackclient package.