Learn Spanish (Latin America): Nos hacemos una seña el uno al otro para coordinar la volea. - We make a signal to each other to coordinate the volley.

While nos usually means "each other," it can also just mean "to us" or "to ourselves." Adding el uno al otro removes any ambiguity and adds emphasis to the sentence. It explicitly spells out the reciprocal action: person A makes a signal to person B, and person B makes a signal to person A.

Why is it al otro instead of just el otro?

The preposition used inside the el uno... otro phrase must match the grammatical role of the action. Because we are making a signal to each other, we need the preposition a (to). When a is followed by the masculine article el, they contract into al.

How would el uno al otro change if "we" referred to two women or a whole team?

The phrase must agree in gender and number with the people involved. If "we" refers to two women, it becomes la una a la otra. If it refers to a group larger than two people, it becomes plural: los unos a los otros (or las unas a las otras). The phrase el uno al otro used here implies exactly two people, at least one of whom is male.

Why do we use hacemos (we make) instead of damos (we give) with una seña?