A few good answers.
The details, without the small talk.
How do I choose a size?
Choose an available size on the product page. Store owner: add garment measurements and size charts to each product listing before selling.
How do I manage an order?
Use My account to view orders placed with your account. Your order confirmation email provides the order details.
What about shipping and returns?
Review the shipping and return policy before ordering. Store owner: publish your actual delivery and return terms before launch.