Hi Brendan, thanks for reading the piece!
What I mean by developing a tagline is summing yourself up in 1 sentence — what you do and who you are. For example, Tony Robbin’s tagline is “I awake the giant in people”.
You could think of it as your personal statement that tells people in a few words all about you and what you do. For example, a writer’s could be something like “I write and create people’s content to save them time”. It’s a pretty simple statement and says exactly what you do and what value you can add.