I downloaded missions and, some mods coop maps but, I don't know where to install or place these files. the name of the files finishes with "coop mod.mis" and, "coop mod.properties". Any suggestions?
open your main il2 folder and open the Missions folder
there are folders for Campaigns/co-ops and single missions
open the coop folder and then make a new folder in there and name it Mods
put the coop.mis and coop.properties files in there
open game
choose multiplayer
choose start a new server
choose coop
choose your new Mods folder
select mission
select plane
Fly!