Acrylics can by used in different ways. They can be used thick, straight from tube, or thinned with either water or a special medium. Liquitex makes a lot of neat mediums for acrylics, stuff to make them thinner, thicker even yet, bumpy, shiny, or matte. All acrylics are waterproof when dry, and can be cleaned up with regular soap and water. If you want to use your acrylics very thin and runny, you may want to look into a liquid acrylic (see the pen and ink section) instead to save yourself time.
There are a lot of brands of acrylics out there. They are generally divided into two classes, artists' quality and student quality. The artists' quality is a very concentrate paint, with lots of pure pigment in it. It's great to work with...you can thin it down to barely nothing and still get bright, vivid colors. You can also mix a lot of colors together before you get "mud" (scientific term for that gross brown yuck color you get when you've over mixed your colors) because of the pure pigments. They are also more expensive. So that brings us to the student quality, which doesn't mean that the paint is bad, it just won't take you as far, that's all. The colors will muddy out faster, and don't tend to be as strong. But if you are using the colors straight from the tube, or with minimal mixing, they work fine! Some common brands for artist quality are Winsor and Newton, Grumbacher, and Liquitex. These companies also make a student quality version of their paints, like the Galleria by Winsor and Newton, and the Basics by Liquitex. You can usually tell which one you're looking at (student verses artist quality) by the pricing...student paints tend to all be around the same price regardless of color, and the artist paints price will vary depending on what color you choose (some pigments used to make a color are much harder to find and grind up than others).
Acrylics can be used on pretty much any surface, from wood to paper to leather. I use acrylics to paint my suede bookcovers, and often use them on paper because they are so waterproof. The only thing you have to be careful about is that because the acrylics are basically a plastic paint, they will tend to curl a light paper as they dry. It is best to use a very heavy paper with acrylics, or else use them thinned on the lighter papers. There are also canvas boards you can paint on, a rigid board covered with canvas and already primed - ready to paint on. But they usually have a weave texture to them, so don't work as well for small intricate works. These and as well stretched canvases (canvas stretched around a wooden frame) are great though for large works.
Acrylic paints work well on watercolor paper, if you are using the paint thick or thin, but want a good rigid surface to work on. Try to get a paper with a weight like 140 lb at least, or better yet the 300 lb, but that tends to get kind of expensive, sometimes up to $20 Canadian per sheet! The good thing is that it is very good archival paper, and they come in quite large sheets, starting at 22" X 30", and can go up in size from there. Very nice brands like Arches, Fabriano, and Lanaquarelle are good to try.