hi @gratefulayn, just go to https://d.tube/ and login using your steemit username and postkey. And then press 'upload video' button at the top right of the page... that's all.
And for your info, you can also integrate your account with dsound (https://dsound.audio), dmania (https://dmania.lo), and steepshot (https://steepshot.io/) the 'instagram like' platform.