what is surfacer and where can i get it

Surfacer is :
http://ipmsfortcrook.hobbyvista.com/Pages/features/mr_surfacer1.html

You can get them in some hobby shops:
Great Models
Hobby Link Japan

HTH.

i know that once, when visiting vermont, we turned over into a walmart and, browsing through the hardware section for paint-related neccesities, I found a very cheap brand of paint-related chamicals called Klean-Strip. so far I have no idea if they work well, but I got thinner and surfacer from them, and they also had stripper and something else. It comes in large, cheap plastic bottles.

you can also get it at
rollmodels

Francois' link gave a good rundown, but one thing it didn't touch on is the product's best use (in my opinion): Creating casting textures, or even rough rolled plate textures. 500 is great for the former, and 1000 for the latter. I swear by the stuff.

Steve's opinion is all right, I just transmit a simple and basic explanation about the surfacer but there are many ways to use this product.

There is a feature of our Pawel Krupowicz (Vodnik) on Armorama about the surfacer :
Easy way to make non-slip surfaces

HTH.