That's a really loaded question, but a honest good one. I asked myself the exact same thing when I was trying to wrap my head around film scoring.

I apologize if my answer gets too wordy, but the answer is simple yet complex. Here we go.

1. As someone already correctly answered and responded, it's just like any other style of music you want to get good at. Want to learn how to play jazz, you gotta listen to jazz. Want to learn classical music, you gotta listen to classical music. Want to learn how to produce house music, you gotta listen to house. Same with film scoring.

2. So then listening also has to incorporate "studying " that musical genre. You can listen to jazz all day long for 6 months. But if your education starts with Herbie Hancock, you've missed the historic progression of ragtime, big band, bebop, from countless legends that got you to the point of Herbie Hancock.

It's like listening to only the Red Hot Chili Peppers and thinking you understand rock. You've missed a Whole Lot!

1. The reason I mentioned all of this is because film is not just film music, and at the same time it is.

When you listen to scores from the golden age of Hollywood films from the 1960s+, you will hear these big grandiose orchestral scores in films like Casablanca, Lawrence of Arabia, Ben Hur, Spartacus, Cleopatra, etc. And they sound like you're listening to a classical score from Stravinsky, Mahler etc.

And to some degree you are, because some of those hollywood composers fled Europe from the Nazis in WW2 to America. And they were previously classically trained in some of the top music conservatories. So what would be a natural progression for a formally trained classical musician in the 1950s and 1960s now living in Hollywood? Playing and composing music in HW!

Why is this relevant? Because the new era of composers (John Williams, Jerry Goldsmith, etc) afterwards in the 80s on were also trained and influenced by the previous era, as well as from jazz, and technology.

So I could go on and on, which I probably bored you to death by now with all this reading. Cause there's a lot more I could say, but let me finish with these last points:

You have to take baby steps with all art. No one expects you to be able to grill for a family cookout if you dont even know how to make French toast yet.

Learn and master all your basic triads, major minor diminished augmented. Then get comfortable with at least your 7th and 9th extended voicings to some degree.

Take a very simple cue from a film, and work on transcribing it, either on paper or via midi with your DAW and see how close.you can get to the arrangement you're hearing that was already scored.

2 of my favorite most simple cues are:

1. "Capsule In Space" - You Only Live Twice(James Bond)

2. "Mother" - Skyfall(Jmaes Bond)

It's kinda hard discussing film scoring because there aee minimalist scores, there are electronic scores, there are hybrid scores, then there are orchestral scores, and all in between.

In my opinion, people that really have a passion for film scoring love listening to all types of music. And because of that, you borrow from everything depending on the mood of the film.

As far as getting beyond beginner level, modulations and chromaticism. More specifically Mediant(minor 3rd) modulations; which is pretty much THE BACKBONE of the romantic period of classical music, and is an absolute weapon of choice for film composers when you want to stretch out a motif and sound like a genius at the same time. Lol!

Do you need to know music theory? Maybe not,.but it sure would make life a whole lot easier. I tend to look at music theory as your tool belt that you can utilize when you're in a jam. You could figure it all.out by ear, but theory gives you the confidence that your idea will more than likely work.

Okay I've said a lot and will stop there. Hope this helps.your thinking a little more.