Alright, so to participate in Mod Night, you need to...you guessed it...
Put in mods.
If you have the game VIA Steam, then go to your Program Files/Program Files(x86), whichever your Steam folder is in. Then go to your Steam folder.
From there go to the folder named "steamapps", then the "common" folder.
Then your SWBF2 folder, GameData.
When at the GameData folder, look for the folder named "addon". If you can not find one, right click and mouse over "New >", then make a name folder and name it "addon".
That folder named "addon" is where you need to extract all the files from the zip that you downloaded from whichever link you went to in order to get these mods.
Do not extract all the contents separately, they all come in the one 3-lettered folder that they should be kept in. Just extract the entire folder in to the "addon" folder.
Once in there, you should be able to join any server playing the mods you put in there.
If you have the game, but not VIA Steam, then everything still applies, except instead of looking for the "Steam" folder, you're looking for the "Lucas Arts" folder inside the Program Files/Program Files(x86) folder.
Have fun with Mod Night!