Does my iPad use USB-C or Lightning?

It depends on the model. Apple introduced USB-C on iPads starting with the 2018 iPad Pro, and most newer models now use USB-C. As a general rule: if your iPad was released in the last three to four years it almost certainly uses USB-C. Older models use Lightning. The quickest way to check is to look at the charging port on the bottom of your iPad — USB-C is an oval symmetrical connector, Lightning is a narrower rectangular connector with slightly rounded edges. If you're still unsure, go to Settings → General → About and note the model name, then check Apple's website.

Can I use a USB-C cable to charge a Lightning iPad?

Not directly — the connectors are physically different and incompatible. However, if you have a USB-C wall charger and need to charge a Lightning iPad, you can use a Lightning to USB-C cable, which has a Lightning connector at the iPad end and USB-C at the charger end. This allows older iPads to benefit from faster USB-C Power Delivery charging even without a native USB-C port.