Here a bunch of switches have been connected together before convergence has happened

Here after convergence redundant paths, paths where two nodes could find parellel paths,
are eliminated from use. The switch with the lowest node number sets itself up as the root switch.

Here a switch has failed. The paths through that switch are eliminated from attempted use

VLAN = Virtual LANS. A switch can be programmed so that ports on the switch are segragated from
each other. This minimizes collisions between nodes on different VLANS. Minimizes Broadcast Domains.

Switches can be virtually combined via trunk lines.
Also instead of many lines to a server a single connection can be used.