Holiday or Vacation?
Vacation is more common in American English and holiday is the British English term. Holiday doesn’t usually have an 's' at the end, except when we talk about the long holiday we have in the summer, at Christmas and at Easter. So, we go on holiday and we have a holiday, but we speak about our summer holidays, Easter holidays and Christmas holidays.
A person who goes on holiday in the US is a vacationer. In the UK, he or she is a holidaymaker.

Tourism or Sightseeing?
Sightseeing is what we do when we go to places that have interesting sights to see. For example, in London, some of the famous sights are Buckingham Palace, Big Ben and the Houses of Parliament, The British Museum and the London Eye. If a city has many sights, it’s often a good idea to go on a sightseeing tour.

We often use the word tourism when we speak about comercial activity, for example, 'Tourism is vital for the Spanish economy'.

A sightseer is a tourist who travels around visiting places of touristic interest, often in organized groups. When you travel freely on your own you’re more commonly known as a traveller.

A tourist guide (also tour guide or courier takes you around, shows you the sights and explains the history and significance of what you see.
If you don’t have a tour guide, you’ll probably need a guide book to explain these things to you.

These days, many people book their trips themselves on the internet. However, you can go to a travel agency and get a travel agent to organize your trip for you. They’ll book the flights, hire a car and tailor-make your holiday according to your needs. A tour operator will also do this. Travel agents deal more with the public and are often agents for many tour operators.

Travel or Trip?  
Travel and trip are often confused by students of English.

Travel is a verb and an uncountable noun. Trip is a countable noun.

We can say ‘I’m going on a business trip.’ and 'I travel a lot'. Using travel as a noun we can say 'My job involves a lot of travel', for example, and 'travel broadens the mind'.

Journey often refers to travel between two places. For example, 'The journey from Paris to New York takes about seven hours'.

Voyage is used to describe a long journey by sea or in space. For example, 'Cook is famous for his voyage to Hawaii'.

Tour is when you travel in an organized way, often in a group. A tour covers a pre-determined itinerary. Tour can be a verb or a noun. For example, 'Pepito is going on a tour around Australia.', or 'The Stones are touring Japan this year'.