Learn Spanish (Spain): Hizo un gesto con la mano. - He made a gesture with his hand.

In Spanish, definite articles (el, la, los, las) are preferred over possessive adjectives (mi, tu, su) when referring to body parts. As long as the owner is obvious from the verb's subject, you use the definite article. Since he is performing the action, it is naturally assumed he is using his own hand.

Could I use the verb gesticular instead of the phrase hizo un gesto?

You could say gesticuló con la mano, but there is a slight difference in nuance. Hacer un gesto usually refers to a single, specific movement or signal. Gesticular tends to imply continuous, expressive movements, like talking with your hands.

Since hizo can mean 'he made', 'she made', or 'you made' (formal), how do we know who made the gesture?

In an isolated sentence like this, it is ambiguous and relies on the translation provided to know it means 'he'. In a real conversation or book, the context from previous sentences makes it obvious. If clarification were needed, you would add the subject pronoun, such as Él hizo un gesto con la mano.

Why is the preterite tense (hizo) used here rather than the imperfect (hacía)?

The preterite hizo is used because the gesture was a single, completed action. If you used the imperfect hacía, it would change the meaning to 'he was making a gesture' (setting the background scene while something else happened) or 'he used to make a gesture'.