Most convenient way to Hiroshima is using bullet train (a.k.a. Shinkansen) from Tokyo (~4 hours), Osaka (~1.5 hours) or Hakata (~1 hour).
Alternatively, Hiroshima Airport (1 hour from city center) is serviced by some domestic and international flights.
Inside downtown of Hiroshima city, tram is the most convenient way of transportation. Taxi costs about JPY 1000 for commutng inside downtown.
Additional information regarding travel, brief history, local foods, etc could be found at WikiTravel.