This command forbids the use of a nickname on the local server for a specific period of time. Use of this command by IRC operators is largely deprecated in favor of forbid which will apply a global qline. Additionally, forbid can also ban the use of email addresses or channels, making it a much more powerful alternative.
Should you desire to apply a qline for some reason, then the command accepts 1 to 3 arguments, the nickname you wish to ban, the duration of the ban, and the reason for the ban. To ban the use of nick1 for 1 second for the reason "Use another nickname.", you can issue the following command:
/qline nick1 1s Use another nickname
Note that not all clients support using this command directly. If you get an error message, you should prepend /quote or /raw to the command. If you do this, you will also need to prepend the : symbol to the ban reason, otherwise only the first word of the ban reason will appear in the qline.