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.
Limited Express Hitachi (ひたち) and Tokiwa (ときわ) are operated mostly between Shinagawa, Tokyo, Ueno and Katsuta, Iwaki via Mito on Joban line. These trains were operated as Super Hitachi and Fresh Hitachi from Ueno station before March 13, 2015. After that, these trains depart from Shinagawa station via Tokyo station. It is much more convenient to get on this train from Tokyo now. These trains connect most of cities along the coast side in Ibaragi and southern part of Fukushima.
If you travel to Mito, Iwaki, Yumoto Hot Springs resort, this train gives you directly transfer from Tokyo, Shinagawa and Ueno.