Reciprocal verbs are used to express the idea of reciprocity - doing something to each other. In Spanish, the plural forms (nosotros, vosotros, and ellos) of reflexive verbs are used to express this idea.

Ellos se hablan demasiado.
They talk to each other excessively.

Nosotros nos llamamos todas las semanas.
We call each other every week. 
 
¿Uds. se quieren mucho?
Do you love each other a lot? 

Some verbs can be used both reflexively and reciprocally, so the expressions el uno al otro or uno a otro can be added to emphasize the reciprocity. Note that these expressions are changed to agree with the subjects in gender and (sometimes*) number.

Nosotras nos pegamos.
We hit each other.
 
Nosotras nos pegamos una a otra.
We hit each other.

Ellos se besaron.
They kissed each other.
 
Ellos se besaron los unos a los otros.
They kissed each other.