Data Designer is the tool that should be used to create a sendable data extension from various tables including orders, subscribers, and product line items. Data Designer allows you to create custom data extensions that can be used as an entry source for a journey. It also allows you to join multiple data sources together to create a single data extension. You can find more information about Data Designer and how to use it here: Data Designer. Automation Studio is a tool that allows you to automate tasks such as sending emails, importing files, extracting data, etc. Audience Studio is a tool that allows you to collect and unify data from various sources and create audience segments for personalized marketing.