If you’re looking for the easiest way to travel around the city, it’s hard to beat the Paris metro. The first line was built in 1900 for the World’s Fair, and there are now 16 lines criss-crossing the city. Easy to use, cheap, and often boasting beautiful stations and entrances, it’s the best way to get around, and the way that most Parisians do.
I like to take photos of the station entrances whenever I see a nice one.
This one is at Bourse.
The metro is super easy to use. All you need to know is which line you want (they have numbers and colours) and which direction you are going in (determined by the station at the very end of the line).
The RATP have an easy to use website, explaining how to get around and the various types of tickets you can buy. I recommend buying either one of the various passes, or a ‘carnet’ of 10 tickets (check the t+ section on the website below). You’ll pay less than if you buy them individually and spend a lot less time waiting around in line. Children under 10 get half price tickets.