Uploaded videos are reviewed before publishing for your account. If you want to add videos without moderation review, an admin must turn off your videos auto-block.
You can import any URL <x id="START_LINK"/>supported by youtube-dl<x id="CLOSE_LINK"/> or URL that points to a media file. You should make sure you have diffusion rights over the content it points to, otherwise it could cause legal trouble to yourself and your instance.