A Suica card is a Japanese stored value card. You get one and top it up with funds and use it in many places. You can read about it at many places in the web. It is still, though, primarily used for taking tr train and subways in Japan. But can also used for buying things at certain stores or vendoring machines.
I find it not as useful as 八達通 in Hong Kong though.
Anyway did this video for purchasing a fresh new Suica card from a machine at any one of the subway stations.