To upload your videos, go to My briefs page and click on 'Upload videos' from the brief you want to upload videos to. If you can't find it, come here.
Then drag in and drop the videos you want to upload in the uploading area (it will turn green when hovered) - you can do this one at a time or as a batch. Alternatively, click anywhere within the uploading area, that will open a window from which you can retrieve your videos from your computer.
You can preview your videos by clicking on them - this way you can do a final check to make sure they're looking tip top.
You can also delete any videos you're not happy with by clicking on the '...' icon in the top right of the video card to reveal the Delete option.
When you're happy, click submit at the bottom of the screen, confirm you're sure and then your vids will be submitted! You can then still watch your videos back and/or upload more vids until the deadline closes.