Once you have a video box or video channel added to your site, it's really easy to add any video from Youtube to your site.
Log into your Wix account and go to your sites dashboard.
Select Video Library.
Click Videos on drop down.
On right hand side hover on the Add Videos button or click the down arrow and a range of options will appear. Click on Youtube.
5. Paste Youtube video or playlist URL.
6. Click Add to Library.
7. Once it has uploaded remember to add it to a channel (if applicable) so that it shows up where you want it on your website.