How do I accept payments like Fiverr?

Hi guys! Kind of confused on where to even start looking for this information.

I'm working on a startup focused towards freelancers who will sell digital products. I, as the platform, want a commission every time a user makes a sale.

My confusion comes from how this would all work from an accounting point of view. Does all of the money come directly to me, the platform, and then I send the appropriate amount to the seller, or the other way around? Or does it all go down at the same time when a user makes a purchase, as in is the payment from the user split into two payments (commission to the platform and excess to seller)?

I want this to look like Fiverr's freelance with commission system.

Thanks for any help!