Welcome to Udimi. I recently started myself. I'll share with you my understanding and hope someone else with more experience can also post and correct any point i may have incorrectly described.
The concept is to create an Optin (aka Presell) page with the hoplink for the product you are selling. This info is provided to the Udimi Seller who connects you with list of potential customers providing you with (Clicks) which you purchase.. Potential customers may either buy right away or leave you their information (email address'/phone contact) gathered from the presell page where you can reach out to them to further sell your product assuming they don't purchase right away. PM me if you need more details. I'm learning as I go too. No need to reinvent the wheel and make the same mistakes I may have incurred. Hope this helps. Good Luck!