First, go to Youtube Free - you'll need to setup a Youtube API key. It's free and takes a few minutes.
They've included a helpful video on how to do it.
Next, click on Galleries. We'll change a few settings.
Gallery Page Size: 3
Number of Columns: 3
Show Pagination: ticked
Show Subscribe button: ticked
Make sure you click the big Save Changes Button after.
Adding a Channel
You can add a Youtube channel by creating a standard Text Block in Visual Composer and clicking on the 'Youtube' button:
There's an option within this to Embed a channel like so:
Copy and paste the link to your Youtube channel into that field and click Get Channel.