We use reciprocal pronouns each other and one another when two or more people are acting on each other.
Rhina and Sam saw each other yesterday.
The boys helped one another do their homework.
They talk to each other in French.
Both each other and one another refer to either persons or things.
They connected the two computers to each other.
High mountains were facing one another.
Each other used to refer to two people and one another to more than two people. However, since this distinction is disappearing in modern English and the two phrases are becoming interchangeable, we may feel a bit insecure when deciding which one to use.
Romeo and Juliet loved each other/one another.
People communicate to each other/one another over the Internet a lot today.
We can also use the possessive form of each other and one another:
Tom and Sally helped look after each other’s/one another’s children.