Create a user
On each User creation, a keypair is generated and user's public key is signed against zinn's certificate authority.
Create a client
You can create a client or accept an invitation from another client. If you're the first user of a client, you have the owner role by default.
Create a vsite
Vsite stands for Virtual site. A Vsite creation is a way to start a coherent cluster. This cluster belongs to a sitegroup, defined by some rules (redundancy of "real" geographical sites, ....).