I definitely imagine travelers are confused in transportation system, especially Tokyo, in Japan in Japan,
Here are some small tips of Transportation IC card for those who need a clarification.
Tokyo, one of the biggest cities in the world, is known for the complicated transportation system. Metro, one of the transportation methods in Tokyo, is no exception in it.
Pasmo is the IC card provided by Metro. You can buy it with 500yen deposit at the Metro counter in some of the biggest stations in Tokyo area, and you can recharge in any station.
This IC card, Pasmo could be also used in the other transportation such as JR, other private train companies.
If you basically go around in Tokyo area using Metro often, I would recommend that you buy a Pasmo card.
Contrary to Pasmo, Sucia is provided by JR. You can get this IC card at counters in JR in all over Japan.
You can recharge it with tickets counter in any stations not only JR, but also other train operators.
If you go around not only Tokyo, but also other cities around Tokyo with middle range distance, I would recommend that you buy a Suica card.
As long as you get either Pasmo or Suica on the first day of your stay, your travel will get much more easier.