Workflow for ecommerce- linking event to a user

MasterG is to be platform for custom shirts where user selects the fabric then cuff, collar etc and then inputs sizing to complete the order.
How do I associate a unique Id with user as the signup or login option is to be on the cart checkout. Another problem I am facing is the workflow to associate the collar type i.e. the event when user selects a collar type with the unique user for the unique order. what i want to achieve is bit similar to this

You don’t need to attach a unique id to the user. This happens automatically when a user signs up / log in. Then, whenever a workflow creates something, the current user will be attached as the creator (see https://bubble.io/reference#Data.Messages.CustomType.Created By)

What you probably should is create a type order, and save the type of collar you want at the order level.