It can be difficult talking about music if you've had no training! Your composer will be able to help you find the perfect style for your needs, but here are some tips that will quickly get you the best results from your soundtrack composer:
Send a reference song. If you have a specific idea of the soundtrack style you want and you can find something that sounds like it, send it to the composer! Just like a picture can say a thousand words, a song that has the mood or style you're looking for can cut straight to the point. You can then personalise the sound knowing you're already on the right path. This is a really fast way to get a sound you want, but also discuss the points below to get something better tailored to you.
Describe the emotion you want the music to create. Adjectives like 'calm', 'energetic', 'tense' and so on can go a long way.
Describe the place you want the music to evoke. Does your game have an Indian setting? Is your film set in South America? This will suggest styles to your composer.
Describe the time, or sense of time you want. Is it in the past? Retro-futurist? Future? Does time need to feel like it is moving slowly, tensely, quickly? Is it a good or a bad thing that time is passing? Dunkirk's soundtrack famously has an almost constant clock ticking sound that makes the passing of time urgent, but also makes us aware that every second spent still alive is lucky.
Did you deliberately create unusual visual effects? Point them out to the composer, who can then suggest ways the music can enhance that effect. Do you want the music to be disorientating? Weird? Your composer can do that!
How long does the track have to play for? Is it just some menu music that won't be heard much, or is it a track that will loop for hours of gameplay?
Is this background music that is really subtle, or do you want a full-on epic theme that the audience will remember? Should the music have all the audience's attention, or be barely noticed?
Most customers really enjoy the creative to-and-fro between them and their composer. If you use some of the advice above, you'll get fantastic results in no time!