Some travellers want to visit as many countries as possible. Yours truly has now visited 98 countries, although there are many ways to count. For example the Traveller's Century Club counts sovereign states as well as certain territories, exclaves and island groups. As of 1 January 2016, the list contains 325 such territories.
In contrast, the United Nations recognizes 195 countries, but this does not include Taiwan, the Holy See and the State of Palestine, nor other entities that are in effect self-governing but have not been recognized by all member states.
The real number of countries lies somewhere in between these numbers. What is not disputed is that there are seven continents in the world: Asia, Africa, North America, South America, Europe, Australia, and Antarctica*.
How can you visit the seven continents in as short a time as possible.
Assuming you live in North America, the first thing you need to do is board a plane to Ushuaia at the Southern tip of South America. Arriving the next day you will have now visited two continents.
Next, board a ship to Antarctica, which will take you a minimum of 10 days return trip.
On day 12, fly overnight from Ushuaia via Buenos Aires to Madrid and join the Madrid to Marrakech tour. At the end of this two week trip you have been to five continents.
From Marrakech fly on Lufthansa and Singapore Airlines to Melbourne. Enjoy a a few days in Singapore along the way and join in on a fine walk along the Twelve Apostles.
Fly home and you have seen the seven continents in about five weeks.
* although even here there are different opinions as some count Europe and Asia as one