This is soft of a more detailed guide, for the easier way, check the main workshop page.

YOU MUST BE THE HOST FOR THIS TO WORK! Your friends and anyone you playing with while you hosting only have to subscribe to this mod, they won't have to run in "insecure" mode or install anything below.

First, you need Sourcemod[sourcemod.net] and Metamod[metamodsource.net], download and extract it to or
Download "Fortnite Emotes and Dances"[ufile.io], unzip and

• put the fortnite_l4d1&2.smx file in sourcemod\plugins folder
  
• put the fnemotes.phrases.txt in sourcemod\translations folder

• Subscribe to this mod OR manually download it and put the .vpk file in
  
  ...\left4dead2\addons\workshop

• Run the game/server with "-insecure" launch option, connect to your server or locally host one depend on where you installed on step 1.
  
• Type !dance or !emote in chatbox and voilà!