3 Easy Steps to Download a User-created MOD:

Step 1:
Download a user-created MOD from Capitalism Lab MOD forum
Most Popular MODs:

The RealWorld Mod is the most popular mod for Capitalism Lab, with over 600 products and 900 customized product images, plus lots of new logos and portraits. It is the essential mod that we recommend to all Capitalism Lab players.

The Capitalism World Mod uses the mod system in a truly creative way, adding an amazing array of new industries to the game, including airlines, insurance, banking and telecommunication, electric cars and even rockets (yep you can build your own SpaceX).

Step 2: 
Unpack the downloaded files to your MOD folder.
i) Open your Capitalism Lab program folder by right-clicking on the Capitalism Lab game icon and select “Properties”, then select “Open File Location” to open the Capitalism Lab program folder.

ii) Select MOD folder under the Capitalism Lab folder. (If the MOD folder does not exist, you may create one yourself. )

Step 3:
Access the MOD interface from the game main menu and select the new MOD to use it.

Click here fore more details

Alternative Method

Alternatively, you may just click the [MOD setting] button from the game main menu, as shown below.

MOD Setting on Main Menu

Then click the [Download MOD] button at the bottom-right corner of the screen, as shown below.

Download MOD lower right corner

The following window will appear and you can simply follow the instructions there to download and load user-created MODs.