yes the node just becomes the first node in the cluster. then you can join others (is a multimaster cluster).
all shareable resources are shared (there is proxmox cluster filesystem that replicates /etc/pve on every cluster node, and that has conf files, dbs, etc.)
this means that if you have a "local" storage, that will be on other nodes too, but it will be "local", meaning a local folder, of course to each node.
instead, a nfs or iscsi share or else will be (if configured properly, see wiki) really shared betwee all cluster nodes.
Marco