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Paper
You can buy paper designed for use with acrylics, like Strathmore 400 Series Acrylic Paper, which is heavyweight and provides enough tooth for acrylic paint.
You can use other types of paper, like watercolor paper, but you'll need to use a very thick paper, otherwise the acrylics will bleed through to the other side and/or the paper will buckle and warp. I would recommend using a fine art paper that is 300lb. For instance, if you look at these fine art papers by Arches, you'll see that there are "weights" ranging from 90lb right up to 555lb.
You can also buy paper with different textures: Hot Press, Cold Press, and Rough Grain. Hot Press paper will be the smoothest, so that is the one I would recommend for painting with acrylics. The Rough Grain paper will have a rough, bumpy texture, and the Cold Press will be a little bumpy but not as much as the Rough Grain. Those little bumps could get in the way when painting with acrylics.
While you can achieve some nice effects by painting with acrylics on paper, the reason I wouldn't really recommend it for beginners is because the acrylics will soak into the paper. Acrylics are hard to blend in the first place, but when they soak into the paper, they will be even harder to blend. Plus you can achieve greater brightness and vividness of colors when you paint with acrylics on canvas or wood. Finally, because canvas and wood are stronger than paper, they can easily handle far more layers of acrylics than paper can.
Canvas
Painting with acrylics on canvas is always a sure bet. While you probably will not be able to find 300lb fine art paper at Walmart, you will usually be able to find artist canvas there which is suitable for beginners.
Most canvases are sold "pre-primed" which means the factory has already applied one or more layers of gesso to the canvas. However, I usually find that it is a good idea to add another layer or two of gesso on my own. Gesso basically adds more "tooth" to the surface of the canvas, making it easier for the paint to glide onto the canvas and stick. It can also increase the vibrancy of your painting to a degree.
To learn more about gesso, read my page that describes what gesso is and how to use it.
Another option is to paint on canvas sheets that come in canvas pads. These sheets of canvas, which are unstretched and packaged as a pad, are usually not archival quality, but they are very economical and convenient for beginning artists.
Wood
Wood is another excellent surface for painting with acrylics. If you are not too concerned about longevity (that is, the painting lasting for hundreds of years), then you can take any piece of wood, apply a few layers of gesso, and then paint on it. This is usually fine for beginners.
However, if you want to make sure the painting will last for centuries, you should use a wooden fine art board such as Ampersand Gessobord, which is already coated in gesso. Ampersand boards are museum-quality and built to last.
Propping up your painting surface
If you paint on paper, unstretched canvas, or a wooden panel, you will need something to prop up your surface as you paint, and then place that on an easel. (More about this in a second.) If you paint on stretched canvas, you can either prop it up on an easel, or you can use push pins or nails to hang the painting directly onto a wall as you paint.
For paper or unstretched canvas, you will need to attach the paper or unstretched canvas to some kind of board. Wooden boards are best, because they are strong, sturdy, and long-lasting. I would recommend one of these hardboard panels because they are very economically priced, at under $5 for a 24" x 30". However, you could also use something like foam board, which you could probably buy at Walmart.
To attach the paper or unstretched canvas to wood or foam board, apply an artist's tape to the corners of your paper or unstretched canvas to securely fasten it to the board. Taping down your paper or canvas ensures that it won't accidentally move while you paint.
Now, you could try propping the board in your lap and lean the top edge of it against a wall, which I have done at times, but this is not a comfortable position for everyone and it's not the most secure. Easels provide the most stability, so I would suggest placing the board onto an easel.
Easels for Beginners
You can get good, lightweight easels for around $40-60. The Bamboo Lyre Easel is a good option. If you plan to work on a large scale, you'll need to spend more money to get a sturdier easel.
If you are working on a small scale, you can get a cheaper tabletop easel, which as the name suggests, rests on a tabletop. A tabletop easel is a cheaper alternative if you will be making paintings that are 11" x 14" or smaller. You can get a decent tabletop easel for $10-20, such as an aluminum folding easel.
