While customers are able to purchase products through the kiosk in more of a self-service fashion, admins can also check out products for customers through the admin site. Here's how:
In your Admin site on the left menu bar, click Store > Store > select the Product you are selling by clicking the Add button on the right of the product > Check out on the right side of the screen.
Next, search for the member by typing in their name in the Affiliate member search box and selecting them from the drop down. Select the payment method.
Visitors can also be checked out. Repeat the same first steps, but instead of searching for an Affiliate member, enter the visitor's information under Charge Visitor / Credit Card or Mark Paid in Cash by Visitor as appropriate on the right side of the page.
When checking out a visitor, always add an email otherwise you could end up with duplicate profiles for the same person.
You do not need to create the visitor as a member first. When you add in the email and name, they will automatically have a Member profile created for them.