each：
det./pron.(兩個或兩個以上的人或物中)各自，各個，每個；
例句：
We see each other every now and again.
我們偶爾相見。
You will each be given the chance to state your case.
你們每人都有機會陳述理由。
We must all try and help each other.
我們都必須努力互相幫助。
They haven't seen each other for years.
他們彼此多年沒有見面了。
both：
det./pron.(與復數名詞連用)兩個，兩個都;不僅…而且…;…和…都；
例句：
They were both only 20 years of age.
他們兩人都只有20歲。
They both had some right on their side.
他們雙方都有一定的道理。
They both said much the same thing.
他們兩人的話大致一樣。
A free trade agreement would be advantageous to both countries.
自由貿易協定對兩國都會有利。