You can than activate the mods you want to play with. It parses your installed mods in the CiV userdir mods directory (usually My Documents\My Games\Sid Meiers Civilization 5\MODS) and creates a list of currently supported mods. The mod manager tries to enable mod support for Civilization 5 multiplayer games. DON'T DOWNLOAD AND INSTAL IF YOU DON'T KNOW HOW TO FIX YOUR CIVILIZATION V INSTALLATION.