Tokyo To Yokohama?

Can I use JR East Pass (Tohoku area) To Yokohama?

Yes if you use ordinary JR trains (not the Shinkansen, and not those of other companies).

I believe if you want to go from Yokohama station to say shinjuku? then you have the Shonan-shinjuku line or the Yamanote.

I advise using google maps from what station your coming from and going to it will show you all the options you need.

In that section, you can take only JR-EAST's train, JR Tokaido shinkansen is NOT, pass not covered.

See the route maps, 1st one is simpler(republished for this Q).
https://postimg.cc/BX2KPc0G

In fact, there are so many rail stations,
http://www.yokohamajapan.com/information/getting-around-yokohama/
http://www.yokohamajapan.com//img/information/access/yokohamarailmap_1...
but I do not know why on this map[PDF], JR Tokaido Shinkansen is not written.

However, not only Tokyo staiton but also places where Shinjuku side is also Tokyo as one prefecture.
http://ameliabusinessdirectory.com/world/tokyo-japan-map/attachment/to...