Suica is the prepaid travel card that can be usaed in JR and Tokyo Metro lines. Suica doesn't give you any discounts but makes the travelling inside Tokyo very smooth as you don't need to go to ticket machines and wonder how much it will cost to go where ever you are going, and either you don't need to use the fare adjustment machines, as long as your card has credit.
Suica is compatible with IC and PASMO, so even if the gate doesn't have Suica logo, it might still be possible to use it. In addition Suica can be used in greater Sendadi and Niigata areas. Suica can be also used to purchase goods in station shops or restaurants.
You can purchase the card and pay the deposit for the card. If you want to stop using the card and give the card back to JR, you can get your deposit back. It is possible to charge Suica card in JR ticket machines and convenience stores.
We recommend Suica if you need to use public transportation often in Greater Tokyo area.