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.