Hamamatsucho is one of the stations on Yamanote line in downtown Tokyo. This station is not a mega station, such as Tokyo, Shinjuku. But this station is the hub of local transportation in downtown Tokyo. JR Yamanote line and JR Keihin Tohoku line connects many places in downtown Tokyo. Tokyo Monorail connects Haneda airport and Hamamatsucho.
And there is subway Daimon station. This stations is different name from Hamamatsucho station. But actually these stations are located in same place. You can catch Toei subway Asakusa line and Oedo line at Daimon station.
Shinagawa is one of the terminal station in Tokyo. It is the transfer point of Tokaido Shinkansen (Nagoya, Kyoto, Shin-Osaka), Keihin Kyuko (Haneda airport), Narita Express (Narita airport), Yamanote line (Shinjuku, Shibuya, Tokyo) and many more lines.