You can use any radd.it or reddit.com URL. This includes subreddits, multireddits, search results, wikipages, or individual posts. Any partial URLs are assumed to be reddit URLs. Multireddits must be public and use the full URL, not the /me/ URL.

You can also use any Youtube URL to add playlists, channels, or users. Playlists always load the latest version while channels and users load the uploaded vids with the most recent vids first. This is not for adding single videos, use the add button under the links instead. (If no links are loaded, use the "Empty playlist" option under Special feeds.)