Most of the time I paint on a canvas that has been stretched over a light wooden frame. The 'canvas' is usually duck cotton covered with several layers of 'Gesso'. The white Gesso substrate serves to protect the cotton material from the elements and from oil paint, if that is the painting medium.
A canvas painting has many advantages. For the artist, the surface has a springiness that affects the brush strokes. Some artists like this, others don't. The rough surface of the course cotton creates a natural texture that gives a canvas painting such a distinctive character. Perhaps the most important advantage of a stretched canvas is its lightness, which means that it is easy to move around. It also means that it won't put much stress on the wall where you hang the painting.
Sometimes I use oil paint as a medium. Oil paint takes a long time to dry and if a project requires fine shading or subtle color transitions, then oil paint can help to achieve the desired effects. However, the long drying time also means that the painting must be stored somewhere for a few months before it is ready to sell. Oil paints have been in use for hundreds of years and remain a popular choice for making art.
More frequently, I use acrylic water based paint. It dries quickly to a very durable surface. It is easy to use and easy to clean up. There are many different brands and colors to choose from. In the end, there is not much visible difference between an acrylic painting and an oil painting. Acrylic paint is a twentieth century invention and the makers keep on improving this medium, and expanding the range of capabilities. I like it very much.
In most cases I plan my paintings before I start painting. Sometimes that means a simple sketch, at other times I might prepare a complex composition or collage of photos and drawings. Next, I transfer the sketch or design to the canvas. This I usually do with a pencil. Some artists like to use charcoal, but I like the fine detail that can be achieved with a pencil. It can take as little as a few hours or as much as a week or longer to get to this point.
As the work continues, I usually take photos. The photos serve as a reference and sometimes I will revert a part of the painting to the way it was because I like that better. Usually I will paint a transparent 'underpainting' before starting the final layers. Most of my paintings consist of many layers. I like the effects of transparency (where you can see a layer of color below another translucent layer of different color). If I don't like what I see, I will paint over. I only stop when I am totally satisfied with the result.
I have started and finished a complete painting in as little as 3 hours, but mostly it takes me several days and sometimes several weeks of labor to finish up. When I am done, I let the painting dry, and then give it two or three layers of varnish. This will help to ensure that the picture remains the same for a very long time.