If you're a startup odds are you don't know who is your audience. Where do you start?
If your product has alternatives people can choose from, look at competitors and keyword research.
But if you're creating something people don't need yet, you don't know what your keywords are yet. Start with the fundamentals. Figure out what you stand for: your values.
Can you find products and organisations with shared values? How does your product fit in this ecosystem? Start a conversation with them.