If I want to visit Drum Tower &, get off at the Shichahai's station.

You need to get out of the Shichahai Station, Exit A2.
After arriving, walk north along Diwai Avenue around 360 yards. Then you will arrive at the Drum Tower.
From the Drum Tower to Wangfujing, it's suggested to take public bus no.82, and get off at Nanheyan Station. Then walk south along South Heyan Avenue and walk east along East Changan Avenue. The total walking distance is about 670 yards.