Getting around Paris is easy.
Paris is well known to have one of the best public transportation systems in the world!
There is the Metro, the city bus, and the inner-city RER underground trains. There are also the SNCF trains which go to the suburbs (and outward to the rest of France and Europe) and leave from the major train stations.
Passes are available in different combinations for convenient travel.
Then there are taxi's and rental bikes everywhere. You can rent a car too, but unless you're up for the challenge, I'd stick to the public transportation!