Alright I'll start with some basic questions.
Is he in a bowl or a tank?
Does he have a heater and a filter?
Did you cycle the tank?
How did you add him in?
Note that his fins are clamped so he could just be cold. Bettas like to be around the typical tropical temperature of 78 farenheit.
You should have your water parameters tested just in case. Most pet stores will do it for free but it's good to have a test kit on hand.