one another “互相”（ 指三者/三者以上之间）。

each other “互相”（ 指两者之间）。

都是相互代词，常作动词或介词的宾语。

例如：You and I should help each other. 我和你要互相帮助。

We should help one another in our class. 我们班（的同学之间）要互相帮助。

My good friend and I often talk to each other. 我和我的好朋友经常交谈。

He and his classmates often talk to one another. 他和同学之间经常交谈。