Texture describes things in a painting. It is easier to give a feel of it with oil or acrylic. Texture can be rough, smooth, fuzzy, slick, gritty, etc. These surfaces can be accomplished by the type of brushes you use or by the use of palette knives. I must admit I use my fingers at times but that is not a healthy thing to do. I was taught it is good to put rough against smooth paint. Using texture that way could fall in the realm of Conflict which is a principle of design. Good or bad, below is an example of rough against smooth in a painting.