Usage: NAMES <#channel>
Show all of the nicknames that are in the specified channel. If you are a server operator and no channel is specified then it shows the nicks of all the users on the network. If you are not in a channel and try to get the names list, users who have UMODE +i set will not show up, but if you are in the channel then you can get a complete list.
Some clients do not show the users in a channel, and so you can use this command to list them after joining the channel. Listing all of the users on the network is rarely useful to do, and is limited to opers to prevent normal users from sending annoying messages to people they do not know.