No to offense to the work that Vektorboson put into his tutorial, but it can seem rather fuzzy. To put it simply, the drop command creates temporary objects, usually particles, that have velocities, colors, etc. For instance, a fire is just a series of "dropped" fire particles that move in a predetermined vector. You can use this command to make fires, dust clouds, napalm
, waterfalls, fountains, rotorwash...basically you can make an enormous variety of visual effects with the drop command. If you want to see a nice usage of the drop command, I'd suggest you de-PBO the Resistance campaign and take a look at the scripts in the "x13BadEnd.Noe" mission.