If you've purchased a product and are having troubles using it, first check the product's documentation to see if you can find an answer there.
If you can't find the answers in the product's documentation you can contact a creator directly with support questions by using the product support button on the product page.
When you click the Create Message button a contact form will pop up allowing you to write a message that will be delivered to the Creator of the Product. Your message will be sent to the creators Inbox and they will be notified of your support question. Once the creator has replied to your support question you will receive an email, then head over to your inbox and you will be able to see the reply from the creator and follow up with the conversation there.