Buy a ready-made canvas in a craft store of any size or shape. A smaller one, 10 by 10 inches or 12 by 12 inches, might seem as if it is easier to paint on, but in actuality a larger canvas may be more in line with your needs.
Decide on colors you wish to use, and whether you prefer to use acrylics or oil paint. Acrylics have no odor, are easy to wash off surfaces and clothes, dry faster and, most important, allow you to paint directly over an area to change a color or fix a mistake. Oils are the complete opposite.
Buy a color chart, easel, paints and brushes. Choose the basic colors first, and use the color chart to determine which colors belong together. Decide if you wish to have paints in tubes or jars.
Think of an object or a scene. Do not think of how it actually looks, just the thought. This is how you create abstract art. Look at a vase, not at how it actually would be sketched, but how you would think it might look. Use only imagination and feelings, and let your hands and mind create. Do not use your thought process. Understand that you are interpreting, not drawing.
Allow the brush to take over as you paint with one particular color. When your thought process stops, you stop. Add another color and shade it; make it lighter at one particular area or heavier at another. Notice that a darker area above a lighter or contracting color will create depth. Experiment with acrylics. If you do not like the feel, just cover it with another color.
Add a bit of yellow to a bit of the red and blend it with a second brush and create various shades of orange. Some areas will be darker and some lighter according to the brush strokes. Use a fan brush to give yet another look to the scene. Expect to use all shapes and sizes of brushes to get different looks. Walk away when you create abstract art. When you return, you will get another perspective.
Stop when you feel the painting is finished. Do not go back to improve or touch it up. Do not overwork your painting, but learn to finish it the exact moment that you feel it is finished. Stop and clean your brushes, then walk away and start another masterpiece.