Adding YouTube videos and thumbnails is easy!

Videos

Add an Enlil YouTube Player block.  Copy and paste the video ID from your video's youtube url (the string of characters immediately after v=).  Adjust the settings as you'd like and your video is ready to go.  100% responsively.

Thumbnails

Add an Enlil YouTube Thumbnail block.  Once again copy and paste your video ID and select your width, setting it to 0 (zero) for 100% responsive width.  By default the block grabs the medium quality default image from youtube.

Optionally, install Magic Data on your site and use Magic Data symbols in the Video ID fields to grab your video ID's from user/page/product attributes.  Set this up for a "video blog" section of a site via page type defaults, grabbing the ID's via Magic Data using the ORIGINAL_PAGE symbol, to create a "Page List Teaser" "video blog" main page, that will display each video in a page list fashion.