YouTube cards were launched sometime ago. Yet I have many folks telling me they did know how to use or what they do.
I will include a screen shot below. If you have a YouTube channel go to video manager click edit on one of your videos and then cards top of the page.
Below is the ways to link a YouTube Card inside a video. You can add a Video Playlist, Promote another Channel, Donations To a Non-profit of your choice, take polls or link your website.
Below is a screen shot of a card linked inside the video.
Help your channel and next time you upload add a card.
PS: Under channel settings then advanced make sure you asscociate your website on your channel to link your website card.