The fireworks_password command is what you use to set a password to drop the fireworks (you don't want just any ninny to come into your server and be able to drop fireworks, do you? Well, maybe you do, so don't answer that
).
You type
fireworks_password PASSWORD in console to set the password, then type
fireworks PASSWORD to actually drop the fireworks.
Say for example you arbitrarily choose ESF for your fireworks password. You would then type
fireworks_password ESF to set the password, then type
fireworks ESF each time to drop fireworks.
Once they're dropped, you launch all on the map that belong to you by pressing your +use key (default B, I believe), then press it again to detonate them.
You could simplify the whole process by putting the command with the password of your choice in your Admin Mod's adminmod.cfg file, and binding a key ingame to the command to drop the fireworks.
Just note that using too many at once can cause the server to crash.