Not sure how things work in Nevada, but in Pac NW you can serve a lawsuit (typically a summons and complaint) without first filing it / paying the filing fee.
Once a person is served they have so many days to respond: typically 20 if they're served in state, 60 if served out of state.
Sometimes a court hearing is scheduled to occur before these timelines expire, e.g. if plaintiff seeks an injunction; a court can also issue an immediate restraining order proscribing certain conduct without any notice to the defendant (typical in divorce cases when case first filed).
If an unfiled lawsuit is served the plaintiff will need to file it if he wants the court to take any action thereon, e.g. enter a default judgment if the necessary time period has passed since service and if the defendant has stupidly failed to appear and / or respond.
The lesson to be learned here boys and girl is do not ignore an unfiled lawsuit if you are served: treat it seriously, because it is legit and needs to be responded to.