In the Concorde there were these scoops positioned at each of the 4 jet exhausts, each scoop was in 2 halves and just as the wheels touched down and reverse thrust was commanded, these halves would snap together, i always thought it resembled a coconut shell lol.

So the basic idea is normally the jet engines blast rearwards, and if course the aircraft goes in the opposite direction, this is thrust. Reverse thrust simply redirects this jet blast, in reality it's not 180 degrees reversed, well I suppose because there a rather large jet engine right there. Instead the jet blast is redirected both up and down and with a forward tenancy, pushing in the direction of travel.

This is a significant breaking force, it supplements the breaks in the wheels, both taking a lot of the strain from them and also adding in redundancy, because the engines are providing thrust anyway, use that to your advantage, save the life of the breaks and use reverse breaking because it does not depend on rubber in contact with the run way things like bursting tyres or slippery runway conditions will not affect it.

All modern jets, I believe, do this. But the old scoops are no longer used, now you will see either flaps open or whole sections of the engine cowling slide backwards. Same basic idea, a portion of the rearward thrust is being redirected forwards. For safety pilots cannot usually use this feature until the weight of the aircraft is on the landing gear, confirming the aircraft is on the ground. But somehow it has happened that reverse thrust has occurred in flight, this is a very bad thing!