All missions come with 2 parts the .mis mission file and the .properties file. Both need to be installed for the mission to function properly.

Having said that you'll need to choose what type of mission this is. Offline or Online.

When you download these generally this information  is supplied in the zip as a read me file. You'll need to unzip both the .mis and .properties file to the same folder

The default paths for Single mission installation are :

C:\Program Files\Ubi Soft\IL2 Sturmovik\Missions\Single\DE

Adding Multiplayer missions

The default path for online dogfighting missions is:

C:\Program Files\Ubi Soft\IL2 Sturmovik\Missions\Net\dogfight\1

As you'll see I created a folder for storing my add-on missions to make it easier to choose them

The default path for Co-Op Missions are : 

C:\Program Files\Ubi Soft\IL2 Sturmovik\Missions\Net\coop\ 1

Installing missions for offline use is  almost just as simple the only twist is the installation for which country and aircraft the mission has been designed.

The default paths are for German campaigns

C:\Program Files\Ubi Soft\IL2 Sturmovik\Missions\Campaign\DE

 for Russian campaigns

C:\Program Files\Ubi Soft\IL2 Sturmovik\Missions\Campaign\RU

All Links are official UBI

IL-2 Official Website

IL-2 Tech Forum

IL-2 General Forum

Unofficial Community FAQ

Game Updates