What is Sin?

Are we born perfect or innocent? Once we seek salvation and choose to follow Christ are we perfect, do we still sin? Is recognition of this sin part of our salvation? Being born and raised LDS I was taught to believe that our quest here on earth was perfection, the closer we were, the better our reward in Heaven would be. I believed the intentions of my heart, the fact that it was pure, or at least I thought it was, assured my reward was celestial glory. As long as my desires were righteous, my salvation was a given. I was oh so wrong!