Contactless payment is the process of tapping or swiping your contactless device, which could be a card or a smartphone, over a reader, which then accepts payment for whatever it is the person is purchasing.
So, to pay for something with a contactless card, you would need to take your plastic card out of your bag and hold it up close to the payment terminal or the RFID reader, and then the signal would be picked up.
Commonly, credit and debit cards are the main two which people use when they want to make a contactless payment, though more and more people use their digital watches, wristbands, and even key fobs to make payments.
As mentioned, there is a restriction per transaction, though this is being increased year on year for many countries around the globe as more and more people familiarize themselves with the technology and this also helps to encourage people to use it over regular cash payments.