how to do i upload a video from my macbook air to a website

That depends on the website.

In general they should have an upload page where you can click a button that opens a Finder window so you can navigate to the video to be uploaded.

As mentioned contact the website in question and ask them how to upload videos to it.

sherifah22 wrote:

how do I upload my lecture videos from my MacBook Air to a website

Contact the website and ask them how to upload videos to their website.