Classical music isn’t always welcoming to newcomers. People who dare to ask questions about the genre tend to preface them with a lot of apologies for their own ignorance and for how stupid they assume their question is going to sound. But once we get past that, there’s one question I hear again and again.

Why does an orchestra need a conductor? And what, exactly, does a conductor do?

It’s not a stupid question. Plenty of people ask it. Whole books have been written on the topic, such as John Mauceri’s recent “Maestros and Their Music,” one conductor’s smart and engaging view of the art. Musicians joke about it — warning colleagues not to look at a conductor they dislike, since his podium antics may prove a distraction to playing the music. Then there are orchestras that play without conductors, including the New York-based Orpheus Chamber Orchestra. Such groups sound very good, but when I hear them play with a soloist, I often come away feeling that something is missing.

No figure in classical music is more iconic than the conductor, or more misunderstood. The authoritarian figure on the podium, waving his arms and demanding that everyone follow him, is the embodiment of the worst sides of patriarchal classical tradition. Yet the conductor also is the ultimate communicator, the person charged with bringing the best out of a hundred musicians to create compelling music. No job in music is harder to quantify, and no job is, when it’s done well, more important.

So here’s a brief look at the function of the conductor.

In the most basic terms, the conductor beats time. Whether the music is written with four beats to a measure, or three, or seven, and especially when it switches from one to another, it’s essential to have someone at the front of the ensemble acting as a traffic cop. In the early days of classical music, this was achieved by banging a large staff on the floor. An essential piece of conductor lore is the example of the composer Jean-Baptiste Lully, who was pounding away with his staff in a performance in 1687 when he hit his foot by accident. Gangrene subsequently set in, and he died of the injury. (Cue jokes about the dangers of art.)

Keeping the beat is still important. The staff of Lully’s day has shrunk into the baton of today, which serves as a useful focal point for musicians glancing up from their scores. The baton, though, varies in size from one conductor to another; Valery Gergiev, the longtime head of the Mariinsky Theatre, famously uses a toothpick. Some conductors dispense with the baton altogether, shaping the music with their hands. The general idea is that one hand is used to keep time and the other is used to signal expression — bringing in the cellos, encouraging the second violins to play more loudly, reminding the winds of a sudden decrescendo. The expressive side of the conductor’s art has developed to a point that it is sometimes hard to find the beat in all of the gestures — Christoph Eschenbach, who until 2017 was music director of the National Symphony Orchestra and is now principal conductor of the Konzerthausorchester Berlin, for example, can be opaque — though musicians tend to appreciate a clear beat when they see it.

Conducting, however, involves much more than beating time. Conducting today is communication: A conductor develops a vision of how she wants a piece of music to sound, and then tries to transmit that vision to 80 or 100 players. Hearing the difference between different conductors’ interpretations isn’t hard, even for classical music newcomers. Test it for yourself on YouTube by comparing the start of Beethoven’s Fifth Symphony as conducted by Gianandrea Noseda, the music director of the National Symphony Orchestra, and by Wilhelm Furtwängler, the legendary 20th-century German conductor. You’ll find plenty of contrasts.

In rehearsal, some conductors try to explain in words what they want before starting to play, but in general, orchestra musicians vastly prefer less talk and more action. Thus, conductors develop repertories of gestures that are as specific to them as their tone of voice.

It’s hard to codify a gesture. Yes, there are some gestures that are nearly universal — beckoning with one hand to get a section to play louder, for example. And some conductors are technical machines, such as Pierre Boulez or Lorin Maazel, whose brains were veritable musical computers, capable of subdividing beats with mathematical precision or hearing minute variations in pitch, and never leaving their musicians in doubt about exactly what they wanted.

For some, a minimalist approach works best: Fritz Reiner, a 20th-century Hungarian autocrat, famously conducted with gestures so restrained and small that once, a musician in the back of the orchestra brought in a pair of binoculars. (Reiner responded by writing “You’re fired” on a piece of paper and holding it up when he saw the binoculars come out.) Leonard Bernstein, by contrast — who was one of the most beloved conductors of the Vienna Philharmonic — leaped around the podium, gesticulated and thrust his pelvis in Elvis-worthy contortions. Yet there’s also a video of Bernstein conducting a movement of a Haydn symphony while standing, his arms folded, using his eyebrows and flicking motions of his eyes.

One of the visual pleasures of a live orchestral concert is watching the conductor and seeing what kinds of gestures he makes and what difference, if any, those make to what you hear the orchestra doing. Some conductors make a great show on the podium but to little effect; others’ every move is reflected in the music. And — as demonstrated by the Bernstein Haydn video — there’s also an intangible communication that flows like an electric current among musicians when the connection has been joined.

In the documentary “The Art of Conducting: Great Conductors of the Past,” which offers valuable insights on all of these issues, a timpanist with the Berlin Philharmonic recalls sitting in the back of a rehearsal, following a score, when he suddenly heard an audible shift in the orchestra’s sound. He looked up to see what had changed and saw that Furtwängler had walked into the room.

“It was his personality alone that created a new sound — just by being in the room,” the timpanist said.

Which offers another answer to the question of exactly what a conductor does: You may not be able to say, but you’ll know it when you hear it.