Brand voice is the way you (as the brand) talk to your customers.
Every time you send an email, write a copy under a post, create video, design a creative, you’re establishing your brand voice.
In today’s world, people want to relate to the brand. Hence, how would you speak to them if you were talking to them directly vs social media. Most likely the answer is, very naturally.
You’re going to avoid all that scientific jargon that loses your average audience. That’s how you should establish your brand voice.