Refilling gas bottles

I am aware I tend to ask the most basic of questions on this forum but thank fellow members for always helping out. We are about to run out of gas for the first time so will be getting a refill. We bought Calor Lite the one you can use in low temperatures (propane) from our caravan dealer. First stupid question.....

Is it the gas that is lite or the bottle?

Can we take it anywhere to be refilled that advertises Calor and does anyone know an approx cost? (Initially I think we paid out about £50 as we had to buy the cylinder).