Youcan 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 yourinstance.
Uploaded videos are reviewed before publishing for youraccount. If you want to add videos without moderation review, an admin must turn off your videos auto-block.