Pick what the code should carry — a link, a Wi-Fi network someone can join with one tap, a contact card, an email, an SMS, a phone number, a location or a calendar event — and the code is drawn as you type.
Change the colours, the module and eye shapes, add a logo in the middle or a caption underneath, then export PNG or SVG. Every code is checked for scannability before you export it, so a logo or a colour that has gone too far is flagged rather than shipped.