Ps: Airport Tickets are different. At the airport you need to buy a airport ticket to go to the city and use one of the pack of 10 to get to another place in town.
And, very IMPORTANT: If you go out from the metro, you cannot use the same ticket to catch a bus.
Pretty simple: You can take multiple buses for 1h30 but only bus. If you change to metro, you can't use the same ticket and vice-versa.
Louvre (check out my video there).
View from Eiffel Tower