How to print from iPad by connecting the Printer with a USB cable

iOS/iPadOS doesn’t natively support direct connection to a USB Printer. Instead, these devices use a network connection to supported printers typically over WiFi - or if explicitly supported by the printer, a wired ethernet connection.

See:

• Use AirPrint to print from your iPhone, iPad, or iPod touch - Apple Support
• Connect an AirPrint printer to a Wi-Fi network - Apple Support

Apple AirPrint is a driverless connection protocol. A high proportion of modern printers intended for Home, SoHo and Business environments now support AirPrint:

About AirPrint - Apple Support

If your Printer does not support AirPrint, WiFi Direct is simple wireless alternative - but will require use of an appropriate App supplied by the Printer Manufacturer (e.g., many HP Printers use the HP Smart App).

A further alternative is to add AirPrint support to your existing USB Printer using a Print Server (e.g., Lantronix xPrintServer - or a Raspberry Pi running CUPS). Both are viable, however, you may find that purchase of a cheap AirPrint-capable printer may be more cost effective.

apples generic printing interface airprint only works over wifi

if your printer support printing over USB from ios devices then it will require a printing app from app store in order for the app to talk with the printer