There are two ways to define your target audience. The first one is to analyze the people who already read, listen or watch you. The second one is to think about who, in theory, might be interested in what you create. Usually when you start a project, some kind of an idea about your target audience is already there, so your first subscribers will, most likely, have the same interests.
After you define your target audience, you have to study each segment of it: its informational background, the environment it exists in, the country or the city where it lives. This can be done using various analytical services, such as Google Analytics
, Sprout Social
A careful analysis will help you create content that will definitely be read by your audience. It will help you understand what the core of your texts, video or audio should be, what will catch your audience's attention and help your reader finish the text.