Using public transport is easy in big cities if you know how to find your way around a bit, all the signs are in English, you won't have any problem understanding. There are lots of signs in the stations, on the platforms, and the twitter data staff is very friendly. All transport is clean, there is no noise in the carriages and people speak softly, it's very pleasant.
The metro lines
Colors and numbers are used to make it easier to read. If you take the train, it will be on time to the minute, you just have to pay attention to the company if you use a subscription card or something else.
The first time, the crowd can be a little confusing, you just need to position yourself correctly on the markings on the ground on the platform to wait for the train.
The bus
For the bus, you just have to signal to the driver, you get on at the back and get off at the front near the driver, the ticket check is carried out at that time.
Several applications can be useful to you, the site www.kanpai.fr is very practical for obtaining information and you can book your train ticket before leaving for Japan with Keikaku, which is very efficient and reliable.