Branch Office, Branch Store
noun
The support shop is the branch office. Presumably this is because the regular "shop" is the "shop" and anything that supports it is the local (branch) office. If it helps, this word has the same meaning as 支局 which you will also be learning in this level.
してん
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
私は毎日、その町の支店に通っています。
I go to the branch in that town every day.
兄は、その支店で中古の車を買いました。
My brother bought a used car at the branch.
私の主人は、ニューヨーク支店の支店長です。
My husband is the branch manager of the New York branch.