Painters put paint on a generally flat surfaces to create 2-dimensional images.
Most painters use brushes to get the paint from a palette onto a canvas. But the brush is not the only way. Emilie Beadle, for example, uses a palette knife instead of a brush to get the paint on her canvasses, and Craig Paul Nowak simply drips the paint from squeeze bottles. There is also spray paint, which still has the stigma of vandalism attached to it. By using different tips for the spray paint cans, painters can achieve highly sophisticated effects.
Some painters, like Jim Pallas in his Art Giants of Detroit series, don't always use exactly flat surfaces, and they almost cross the line into sculpture.