Pro is a Latin root word meaning for. If you make a list of pros and cons, you are listing the reasons for doing something and the reasons not to, respectively.
Pro is also the shortened form of the word "professional," often referring to professional sports. If your cousin plays college basketball — and he's really good — he'll have to decide if he is going to turn pro or finish college first. The shortened form isn't always about sports, however. You might handle your little sister's bicycle accident like a pro, cleaning her up, sticking bandages on her knees, and handing her a lollipop.