Here's a breakdown:
* Soy: "I am"
* un poco: "a little"
* extraña: "strange" (feminine form, used because "soy" is a feminine verb)
The phrase is used to describe someone who is slightly different or unusual in some way, maybe in their personality, interests, or habits. It's often said in a lighthearted or self-deprecating way, acknowledging a quirkiness without being overly negative.