A bit confused on this motion tween

the motion tween (in the centre) that is animated here at: http://luvgalz.kimasa-crew.com/lg2main1.html.

I know this is motion tween but its like “revealing itself” like a sliding door. I try to do it but with my way,

  1. i made an image of my own and set to width: 1.0
  2. i created motion tween.
  3. on the last frame of motion tweening, i set the image to its original width.

Is this how to create it? … it seems a bit different.