We don't use 'holidaymaker' much in the UK either - we would often say tourist too.

Travel agents help plan the trips for you, as in booking flights, hotel, tours, etc. Tour operators are the people who show you around the city or wherever you are visiting on that trip. We don't use the word Holidaymaker in the US, but in the UK it is someone who is on vacation. In the US we'd say traveler or tourist.

It's clear from the set of words that you have here that you've learnt this vocabulary from a British source, so I'll give you the GB English definitions: Holidaymakers are people who are on holiday : tourists or visitors to a region. A tour operator is a holiday company. A tour operator negotiates contracts with suppliers - airlines, hotel chains and so on - and creates package holidays for tourists. A travel agent, in the past, was the tourist's usual means of booking a holiday. Travel agents used to have outlets on high streets - shops with pictures of holiday destinations in the window, and colourful brochures for people to take home. In the past, travel agents would often contact the tour operators to book the flights and hotels on behalf of the holidaymakers. Many years ago, I worked for a tour operator in London, and this was how it used to work - the tourist/holidaymaker made the arrangement with the travel agent, the travel agent made the arrangement with the tour operator, and the tour operator purchased the flight seats from the airline. Nowadays, this doesn't tend to happen. There are fewer and fewer travel agents around, and most members of the public book directly online with the tour operator or airline.