You can paint on anything, canvas, paper, board but my preference is canvas. There are a huge amount of different canvases out there, I paint on a cotton duck canvas (you can tell by looking on the back - it has speckles), it's a tight weave so lovely to grip paint but also a smooth surface to paint on.
You don’t need to buy cotton duck though, so I'll give you a few pointers to buy your canvases.
If you are buying online always check for reviews. There's no better way of telling how good (or bad!) a canvas is than looking at the views of people who've already bought them. Canvases don't need to be expensive to be good quality, and price isn't always an indicator of quality.
If you're buying canvases from an art store or shop try flicking it. It should be tight like a drum skin, if not you're best avoiding it, as it'll get looser once you start painting on it.
Check the weave direction, it should go straight up and not be at an angle (the canvas hasn't been stretched properly if it's at an angle).
All canvases should be primed once it's been stretched onto a frame. This is done with glue or gum mixed with white paint, and keeps the canvas tight. The label should tell you whether it's primed or not - always try to buy primed canvases (simply because it's less work!)
Landscape or portrait? Think about the shape of your image and try to choose a canvas to fit it, I love painting on square canvases and large landscape shapes, almost any shape is available.
If you look at a blank canvas and you feel intimidated, colour the whole canvas. Sometimes I paint mine red or yellow, sometimes dark blue. Colours react better against other colours, white can be flat so get some colour on it.
The first layer on my canvas is usually a layer of any oil colour, adding a bit of white to a colour with big brush strokes can really start an image off. (You can also do the same with acrylics)
If you're still feeling a little intimated get some chalk and draw a basic image to paint, whatever makes you feel more comfortable.
Get a couple of layers of colour on, don't worry about the image - that will come next!!
Go for it!!