I suggest you go to the library and get as many bonsai books as you can and READ THEM. The Internet can be very very confusing, and unreliable as you can't really tell who is experienced and who is just talking the talk to impress others. Books are typically written by people who know what they're talking about. Do a search here on "good bonsai books" and you will see some of the titles.
Good starter plants include boxwood, any kind of elm, really any deciduous tree species that is grown as landscaping in your area (which is an important factor when winter comes and you have to store them during their dormancy period). Japanese maples are a good choice too. Trident maples are even better and are pretty indestructible. You can get seedling Trident maples and others from a number of sources online including here:
https://kaedebonsai-en.com/shop/product-category/bare-root-seedlings/
and here:
http://www.internationalbonsai.com/page/1442817
as well as a few other places too.
Pines are not really beginner's trees, as they can be a bit quirky in designing and care. They're not as straightforward as deciduous trees. Roses are not a good choice. They don't produce new branching as readily as elms and other trees. They also have thorns, which makes working on them a pain, literally.
You have to do something about your soil. It is the engine that runs your tree. Crappy engine means crappy or dead tree. The topic of soil is a spirited one, as many people have their own recipes and preferences. By and large, however, a bag of bonsai soil from a reputable vendor online is more than adequate starting out.
This is pretty good and you can get it from Walmart.
http://www.walmart.com/ip/38363132?...70543832&wl4=&wl5=pla&wl6=81462550832&veh=sem
This bag seems expensive, but you can probably pot a few medium sized trees with it.