iOS devices can only print directly to AirPrint printers. All AirPrint printers are wireless but not all wireless printers are capable of using AirPrint.
To print directly from an iPad / iPhone you will need an AirPrint compatible printer or another device to act as a print server. That can be a Mac computer running Printopia ($19.95 with free trial) or handyPrint (donation - supported). The Mac must be "on" but may be asleep for them to work. Equivalent PC options may exist but you're on your own finding them.
You can also buy this standalone print server:
The xPrintServer Home Edition will support a directly connected USB printer. The Network Edition will support any network printer.
These options enable you to use any printer available to your Mac, even older ones that may predate AirPrint by decades.
Otherwise you will need to buy an AirPrint printer or multifunction device.