Things people are identified by:
Name, gender, race, sexual orientation, religion, nationality, appearance, education, age, upbringing/childhood, money/class, political beliefs..
You can talk about any of those, about events that happened linking those points. Ex. Age could be about being a teenager and how that makes your identity. For nationality i would write about events that point out from where I am from. Or you could talk about when you maybe found out your sexuality and how that shapes you today and makes you you. Include loads of anecdotes.
Hope that helps :)