Read more about the line in English Wikipedia: Yokosuka Line

The name Yokosuka line is used both for the railway line Ōfuna - Yokosuka - Kurihama and for the train service running Tōkyo - Yokohama - Ōfuna - Yokosuka - Kurihama.

At Tōkyō station, Yokosuka line uses an underground station connected with Sōbu line.
Between Tōkyo and Shinagawa, Yokosuka line runs underground parallel to Tōkaidō and Keihin-Tōhoku lines, stopping only at Shimbashi. This section is officially a part of Tōkaido hon line.
Between Shinagawa and Tsurumi, Yokosuka line uses a section of the Tōkaidō line called Hinkaku line. Yokosuka line and Shōnan-Shinjuku line between Nishi-Ōi and Yokohama are the only services using the Hinkaku line.
Between Tsurumi and Ōfuna, Yokosuka line shares a dedicated double track with Shōnan-Shinjuku line along Tōkaidō hon line.
At Hodogaya and Higashi-Totsuka stations, it's only the Yokosuka line tracks which have platforms.

Read more about the line in English Wikipedia: Hinkaku Line

The line is used by the Yokosuka line service, the Shōnan-Shinjuku line service and by the Sōtetsu JR Link service.
Between Tōkyō and Shinagawa, the Yokosuka line tracks are also used by Narita Express trains bound for Shinjuku. They run between Shinagawa and Shinjuku at "Yamanote freight line" tracks parallel to Yamanote line.

There are no passenger platforms at Tsurumi station. All trains continue into Yokohama using a dedicated double track.
Details about traffic pattern, connecting lines etc. can be found in the sections for Yokosuka line and Shōnan-Shinjuku line .