I have a strong body, big shoulders, big bones, and big wrists. Never been to gym?

[Chi Town Represent]

Well everybody's always telling me that. And I have a little fat. I need help I honestly don't know what to do. When I take off my shirt my stomachs flat and you can see a form of pack, but I have fat covering it. My back is curved and I have chest fat and fat under armpits. My chest fat isn't hanging down tho. I'm a 17 year old boy btw.
I should have been more clear. What do you think i should do? Work on? And how has my body become like this? when I never went to a gym