Are there good ways to get my body fit without buying anything?

I have been lacking in my physical abilities for a while.I have scrawny arms and a loose belly around the middle.I can't even do a push up without stopping midway because my shoulders get so tense I can't go lower without falling onto the floor.I also lack the arm muscle to do a pull up.I'm not overweight,I'm at a healthy weight,but it seems most of my muscle is in my legs.Are there any fun sports that would stretghen my weak spots?