Most models of iPad require a Power Adapter rated at 12W or greater to reliably charge. Many of the more recent models are supplied with a 20W USB-C Power Adapter.
Depending upon your iPad model, the iPad will either have an Apple-proprietary Lightning connector - or a USB-C port.
Charging cables must obviously match the equipment that you have. In essence, depending upon your Power Adapter(s) and iPad model, you are going to need one of three cable types:
1) USB Type A to Apple Lightning
2) USB-C to Apple Lightning
3) USC-C to USB-C
Each of these cable types are typically available in 1m or 2m lengths.
Be aware that if you have a recent model iPad that features a USB-C port, then the iPad supports USB PD (Power Delivery) Fast Charging. When used with a compatible Power Adapter (as are all Apple Power Adapters that have a USB-C connector), your iPad can charge much faster.
Non-Apple Power Adapters, regardless of power rating, might not support USB PD, but instead a different (non compatible) fast charging standard. These Power Adapters, if they work at all, will be unable to charge at any greater than 12W (2.4A @5V).