One example of doing this would be to promote a product as an affiliate (from Clickbank, CJ, Etc.)
and then post a video on YouTube that advertises the product and put a link in the description...
Make sure it's your affiliate link OR send them to your website that has your affiliate link(s) on it...
Traffic from YouTube is free and signing up with Clickbank is free so there is one perfect example.
To your success,
Shane