Texture is a very important quality of art. In terms of art, there are generally two kinds of texture: physical and visual.
Most non-digital art--anything we can touch or feel--has physical or actual (tactile) texture. Any artwork that doesn't exist solely within a computer monitor or projected image has actual variations upon its surface. Depending upon what the artwork is made of or covered with--canvas, fur, feather, wood, metal, glass, plastic, etc…--its surface can be rough, smooth, bumpy, sharp, or a mix or one or more textures. Depending upon its texture, artwork often conveys a mood or sensation. Rough or striking surfaces like tree bark, scales, spines, wrinkles can excite our eyes and make our thoughts race and become ever more active. On the other hand, smooth surfaces can encourage us to think of restful situations and calm us.
Visual texture is just an illusion. It’s used to make our minds believe that a digital image has a particular physical texture. Skillful digital artists use light, shapes, color, and line to create a sense of texture that looks real enough to make us imagine a flat, 2 dimensional object can be actually be experienced through the sense of touch.
Andy Anderson (via AdobeTV's Learn Photoshop Elements channel) provides viewers a simple yet powerful demonstration of how to apply one-click effects, textures, and frames. In a hurry? Go to 02:07 to skip directly to the texture portion of the video.
Also available via AdobeTV is Creating Custom Brushes, a 4 minute long video by Richard Harrington that explains how to create a texture brush.
Along with the different elements of art, the BBC's BiteSize Art & Design site also presents a concise description of texture.
The J. Paul Getty Museum's description of how to analyze the formal aspects of a work of art includes a brief explanation of the concept of texture.
Though it was written in 2011, Jon Savage and Simon H. of Smashing Magazine share a must-read online article titled The Whys And The Hows Of Textures In Web Design.
Texture Online offers a wide range of different color palettes, patterns, and textures that are available for download.
Along with all manner of information about visual design basics from the Usability.gov, visitors to the site will also learn about texture.