“Zen” is the name of one sect of Buddhism and sometimes refers to Zen meditation (zazen). There are some 75,000 Buddhist temples in Japan, among which some 2,000 are those of Zen Sect.
There are three principal schools of Zen Sect in Japan. Those are Soto School, Rinzai School and Obaku School. (Obaku School was branched from Rinzai School.)
Each school has its own English website in which its history and doctrine are well explained.
The website of Soto School：http://global.sotozen-net.or.jp/eng/
The top page
If you are interested in zazen, click the icon below left on the top page (indicated with a red circle) which is an entrance to the page of “Zazen”. How to do zazen is well explained here.
A video for seven minutes with English subtitles is also uploaded on the same page which shall give you a concrete idea of how to do zazen.
The website of Rinzai and Obaku Schools：http://zen.rinnou.net/
The top page
The center icon on the top page (indicated with a yellow circle) is an entrance to the page of “Zazen”. As same as the site of Soto School, how to do zazen is well explained.
Video “How to do Zazen” is also available but the narration is only in Japanese without any subtitle.
The temples of Soto School which hold zazen sessions for foreigners (principally for English speakers) are shown on the top page of Country-Japan. This information is cited from the website of Soto School. The information on zazen sessions for foreigners by Rinzai and Obaku schools shall be uploaded as soon as it is obtained.