Useful websites:

http://www.firewall.cx
https://www.gns3.com

Commands:

show int status (which port, vlan)
show vlan (on switch)

show int des (all descriptions)
show ip int brief (all ip interfaces)
show hard (hardware)
show ver (version)
show environment
show ? (all show cmds)
show cdp (neighbours)
show lacp
show int p0 (port/channel)
         port-c
show users
show utp status (trans/client)