“How did you find out about this?”
You go to an event for people who are interested in learning and studying English. You introduce yourself to someone and ask them this.
How did you find out about this?
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This means to learn about something for the first time. It also carries the sense that you have discovered something that other people might not know about.
This band is awesome! How did you find out about them?
To share a specific idea (rather than a general topic) that you found out, the way to express it is "find out that (clause)":
My wife found out that one of her employees was stealing from her.