each：
det./pron.(两个或两个以上的人或物中)各自，各个，每个；
例句：
We see each other every now and again.
我们偶尔相见。
You will each be given the chance to state your case.
你们每人都有机会陈述理由。
We must all try and help each other.
我们都必须努力互相帮助。
They haven't seen each other for years.
他们彼此多年没有见面了。
both：
det./pron.(与复数名词连用)两个，两个都;不仅…而且…;…和…都；
例句：
They were both only 20 years of age.
他们两人都只有20岁。
They both had some right on their side.
他们双方都有一定的道理。
They both said much the same thing.
他们两人的话大致一样。
A free trade agreement would be advantageous to both countries.
自由贸易协定对两国都会有利。