Most of the Android and Apple mobile devices have a 3.5mm stereo jack connector to connect standard wired headphones. If you device does not have this connector, you can still connect your existing wired headphones through an adapter. However this adapter needs to be compatible with your device charging connector and in most cases it is USB-C connector on Android and Lightning connector on Apple devices.
Some of the devices have this adapter already bundled and you received it with your phone or tablet. If you don't have this adapter, you can purchase these adapter worldwide in electronic stores, mobile phone stores or e-shops selling mobile phone accessories. The price is less than €15.
Please choose a solid brand for this adapter and if possible and avoid buying the cheapest one from "noname Chinese brands". We had some cases when these adapters simply didn't work.
If you prefer, most of the mobile devices manufacturers sell these adapters as well. They are a bit more expensive than other brands, but on the other hand you have much batter compatibility.
Just for your reference, here are few global links to USB-C adapters:
And here is the link to Lightning adapter:
If you can't purchase these adapters from your location, try to search for "3.5mm to usb-c adapter" or "3.5mm to lightning adapter" and select a local store where you can buy it. Please note that this adapter must be stereo and not mono. (it is very rare, but we found some noname mono units as well). If you choose a branded unit, you should be OK.