Identity is something everyone has, but you might not know what your identity is. Your identity depends on what you do, what gender you are, how you behave and much more.
An identity isn't something that is always the same, you can change your identity if you want to. Your identity can be based on your gender, your culture, ethnicity or sexual orientation etcetera.
I once saw a short clip (from a TED Talk) of a girl that had a very rare disease which made her incredibly skinny. This girl had it tough growing up since she looked very different and unique.
Her childhood was hard since she got bullied and picked on in school, but once she grew up she decided she was fine with her looking that way and said that she wouldn't let anyone else decide who she was or what her identity was.