Tourist maps of Tokyo usually have at least a partial subway map in an inset. Hyperdia would probably work, but it might be overkill if the OP just wants to go from Tochomae to Shibuya, and it doesn't give you a pictorial overview of the system.

Every station has a map of the system labeled in Japanese, and some of them have a map labeled in English. Signs within the subway and commuter train stations are all bilingual.

There's a book available in English-language bookshops that is a guide to the Tokyo subway system, and the Kodansha Tokyo City Atlas, which is partly outdated but still mostly accurate, has two transit maps, as well as enlarged maps of the principal tourist areas, complete with indications of which exit to take for which destination.

I, too, recommend getting a Suica or Pasmo, both of which work like London's Oyster Card.