What is the main purpose of clickbank?

To sell other people's digital products for profit. It is one of the truest forms of affiliate marketing where you receive a commission selling other peoples products.

You can also create your own digital product (ebook for example) and post it on Clickbank offering others a commission every time they sell your product.

Either way, follow the rules, research any product you may consider selling, and provide value to your customers! There's a lot of junk out there.

All the best!