Texture is a rastre image (bitmap), which provides 3D-models with color, bump and other tangible properties of the surface.Textures are applied to the polygon surface. Using the textures, it is possible to create scars on the skin, folds in clothing, small stones and other objects on the walls or ground.
The quality of the texture is determined by the number of pixels at the minimum unit of the texture. The quality of final render of the 3D scene is heavily dependent on the quality and resolution of the textures.
Textures come in different formats, they can be RGB, using the alpha channel (RGBA), monochrome and others.

Creating textures for 3D-models
Currently, there are two main ways to create a texture:
- Production from scratch in raster graphics editors (Adobe Photoshop, Gimp, Painter, etc.) or from existing raster images (photographs, drawings , etc.).
- Production of textures in specialized programs for drawing textures directly on the surface of the three-dimensional model.
Both methods are now widely used. Both the first and the second methods allow to create high quality texture models.
An example of software solutions, which can immediately create textures: MARI, Mudbox, Zbrush, 3DCoat, BodyPaint 3D. These programs solve the problems of seams and allow the artist to fully concentrate on the creative process. Also a plus is that these programs not only allow you to create different types of textures, but also instantly see how certain textures affect the model.

Textures and geometry
Except for procedural textures all the textures (created from scratch or already existing) should be applied to the object following certain rules. Textures are applied to the three-dimensional model using a coordinate system. Even though the two-dimensional images are based on the XY coordinate system, texture superimposed on the object is based on the U (horizontal) and V (vertical) axis spanning the surface of the object. Texture mapping method will depend on the type of geometry of your object.

Texture mapping and projection
Texture mapping allows to detail the simplest objects without overcomplicating the model's geometry.
Texturing (texture mapping) determines the way in which the image texture connects to the surface of 3D-model. It depends on the position of an object in space. You can not just apply a texture to the surface, without taking into account the distance to the object and its orientation relative to the viewer. Such a scene would look bad.
The most common methods of applying textures are:
•  Planar mapping is a direct projection of a texture from a certain point in three-dimensional space. This method is widely used for applying the texture map to flat surfaces (books, flooring, walls);
•  Cylindrical mapping - the texture is wrapped around the geometry of the model about the same as the label is wrapped around a tin can. This method is used for texturing cylindrical objects
•  Spherical mapping - similar to cylindrical mapping, but the top and bottom of the texture get connected, in some cases distorting the image. Often such seams get hidden by a secondary object. This method is most suitable for texturing faces, balloons, balls, planets, and other similar objects;
•  The cube overlay - an image is projected onto an object from six different directions, each corresponding to the plane of symmetry. This method is suitable for texturing objects such as buildings, boxes or interior rooms.

To project a repeating pattern on the model, it is easier to create a small image and then repeat it over the surface of the object.  This way it's easier and more productive to create surface textures for big objects. Furthermore, small tile images take less space in the memory. However, tiling has its disadvantages. The images may look too uniform, and grass created in this way will resemble the grass carpet instead. In addition, seams will appear between the edges of the tiles, which will need to be covered by something. (But this can also be a plus when creating tiling for the kitchen walls, for example)
In such cases, so-called seamless textures are usually used. They have a picture with an infinitely repeating pattern, which match with no defects even if duplicated many times.

Working with layers
One texture is often not enough for complex tasks - in this case many different textures are used together. For example, you need to create an old log. Bark can be used as the base material with appropriate parameters assigned.Then you can add a level showing the rough surface areas, another layer for moss, third and fourth with cobwebs and dirt and dust. Combining individual texture layers, you can create an infinite variety of options for the appearance of your object.