Try out FL Studio (PC only). Here's a free demo: http://www.brothersoft.com/fl-studio-66439.html
Check out this video of an example of how music is made with FL Studio: http://www.youtube.com/watch?v=Rg3FUZSdgj8
If you need help getting started with it, press F1 while it's open or visit a site like youtube and watch tutorials like this:
http://www.youtube.com/watch?v=tqZgBVx2w_Y
If you decide to purchase one of the full editions, here's an instant 10% Discount you can use when you buy directly from the developers of FL Studio, Image-Line:
https://support.image-line.com/jshop/shop.php?offer=Default&promo=BFHEHAH486
You get free lifetime updates for the products you purchase, so you'll get FL 10, 11, 12, ect.. free once they are released. You also get official forum access at http://forum.image-line.com/
enjoy and have fun with making ambient music!