Once you are at the salespersons desk, they will probably record information about the type of vehicle you want. More importantly to them, they want to know WHY you want the vehicle. The reason they do this is so that they can learn your underlying motives for buying, and will incessantly repeat how their vehicle satisfies your needs.
For instance, if you have kids, they will harp on the safety features. If you are environmentally conscious, they will highlight the low emissions. While this is not bad in of itself, just be aware that they may later try to whip up your emotions over the vehicle based on the information that you provide at this stage. They do this to make their sale.