See:
Apple AirPrint is a driverless connection protocol. A high proportion of modern printers intended for Home, SoHo and Business environments now support AirPrint. Check your printer model against this list:
About AirPrint - Apple Support
If your printer is not compatible with AirPrint, your iPad will not be able to print directly - even when using an AiPort Express to provide a WiFi to ethernet bridge connection to a network printer.
Some printer manufacturers have a suitable companion App that provides Print capabilities for mobile devices, often using a web-based print service. Others can print directly if the App supports other network printing protocols. By example, many modern HP Printers use the HP Smart App - available in the App Store:
https://apps.apple.com/gb/app/hp-smart/id469284907
To print via the AirPort Express, you’ll need either a computer to provide AirPrint services - or a dedicated AirPrint Server Appliance on your network. One example is the Lantronix xPrintServer.
The remaining (and potentially cheaper) solution is to simply replace your printer with one that is AirPrint capable.