Leads → Quotes → New quote. Also Convert to quote on a mockup session or a saved design.
Prefer the storefront when the design matters
A manual quote has no canvas: no colors, graphics or print files can be generated from it. If the garment needs to be produced, build it in the storefront (use Open in customizer on any quote as a starting point, or send the customer the link) so the quote carries a real design.
Can I attach the customer's PDF or artwork? Not on a manual quote. Put the link in internal notes, or ask the customer to upload through the storefront.
Change the quote number format. The prefix defaults to QR; there is no self-service field for it — ask support to change it. Numbers are PREFIX-YEAR-0001, unique per workspace.