Is it true the army boosts your confidence and social skills? And did you have any shy teammates that became confident?

If it's specifically Infantry that you're talking about then 100% yes to both questions. It doesn't matter how confident you think you may or may not be, as early as completing Basic Training you will find out allot about yourself that you never knew. You'll also find you can approach almost any task and any person with a newly found confidence and competence. I can also tell you that something has gone terribly wrong if you don't find yourself very socially skilled after a years service. When you deploy around the world to work with other NATO forces, all the while being part of a Platoon that can consist of every culture from across the country and even commonwealth countries, it would be pretty impossible to not have a decent set of social skills. Contrary to what some people might tell you, the shy and un-confident are just as welcome to join us; they will catch up. I know this from experience because the shy one your're asking about was me 6 years ago.

Whilst socially confident, when i joined the Army at 16 up to the point of becoming a Non Commissioned Officer (NCO) I found it very difficult to communicate to large groups. Having reached the rank of Warrant Officer Class 1 I can say with certainty that the Army develops and enhances your confidence in all aspects. Good luck