What are those screens that photographers take photos in front of called & so they have them for amateurs to take home photos?
Do you mean back drops? You can find those in photography equipment site. Try BH Photo or Adorama.com
In addition to the sources mentioned by joanmn above, you can also find a full selection of studio backdrops & lighting equipment at reasonable prices on Ebay, however it should also be mentioned that studio lighting and backdrops is a complete science unto itself. Before we could even begin to offer advice we would need to know what kind of photos you are trying to make.
If you are trying to shoot portraits you can generally get by with a 6' x 6' backdrop, whereas if you are attempting to take full length fashion photos you would need something in the order of a 10' x 25' seamless paper backdrop. On the other hand, if you are attempting to take table top photos of products for advertising you can easily get by with a 2' x 4' backdrop.
I have recently been experimenting with a setup to shoot photos of all my camera equipment to document it for insurance purposes and perhaps an item or two to list on Ebay.
Although I am still experimenting with the lighting, I have been using standard "Felt" fabric as the background. I found that felt is available in a wide selection of colors at Joann's Fabrics in 72" wide rolls for $4.95/yd. I bought one yard each of Red, Green, Blue, Lt.Brown and white to use as backdrops for my table top studio work, and 2yds each of white & black to make a 6'x6' portrait backdrop.
I am attaching one of the first photos I took with this setup to give you an idea of how the backdrop looks. I love the felt because it makes a non-reflective surface.