how much salt should I put to a 3 pound chicken

I love to well salt it with kosher salt, as in this Thomas Keller method. Well salt the interior, and use about 1 Tbsp on the outside.
http://www.epicurious.com/recipes/food/views/My-Favorite-Simple-Roast-Chicken-231348

I don't cook with salt, after the chicken is done and carved and plated, I sprinkle with a bit of sea salt as a top-dressing.

One note of caution: Depends if it is kosher/sea salt flakes or plain iodized. In my experience 1 tbsp plain ~ 1 1/3 to 1 1/2 tbsp kosher/sea salt.

If you're roasting the chicken, you'll probably want about 1 tablespoon of salt. Generously sprinkle salt over the chicken skin (and inside the cavity) so that it's uniformly distributed. When the chicken comes out of the oven, the salt will have helped create a crisp, flavorful skin (and you'll still be able to see the salt baked onto the skin).