The trams mostly go around the perimeter of the city, making a giant circular shape, while the RER (which stands for Réseau express regional, “regional express network”) is a system of commuter trains that go through Paris, but also extend out into the surrounding regions in île de France (which is the French administrative area that Paris is in – it’s about twice the size of Door County).
If you want to travel elsewhere in France, it’s also likely that you take a train. There is a dense network of intercity trains, including the TGV bullet trains (Trains à grande vitesse, “high-speed trains”).
It’s certainly nice not to have to drive. I never realized how tiring driving can be until I didn’t have to do it anymore! It’s possible to get practically anywhere in Paris in at most 45 minutes, thanks to the metro (and there’s an official app that will tell you which lines to take to which stops depending on where you’re going which is very helpful), which is probably faster than travel by car anyways, given the downtown traffic.
One of my favorite things to do when I have time is get on a RER train and take it to the end of the line which usually means you end up in the countryside somewhere way outside of Paris. One evening during fall break, I took the RER B as far south as it goes (it was about an hour-long ride – I found myself in a small town (think Bailey’s Harbor size, roughly) called Saint-Rémy-lès-Chevreuse. It was very quiet and pretty, a welcome respite from the relentless energy of Paris.
The only annoying thing about being reliant on public transportation, in my opinion, is that it can be very, very crowded sometimes.
