From BlenderWiki

Texture Channels

Description

A material can contain up to 10 Texture Channels, which are layered in a stack.
Each texture channel contains informations about the texture and its 'mapping' on the material, which describes how the texture is positioned on the object's geometry, and how it affects the material properties. A channel can be selected by clicking on it in the stack. By selecting it, you make it active.

Channels Options

Empty Channels

If there is no texture currently in the active texture channel, the following options are available:

Add New

Add a new texture to the active texture channel

Select an existing texture

Choose an existing texture from a list, to insert in the active texture channel.

Channels with Textures

If the active texture channel contains a texture, further options are made available in the Texture panel, and in two additional panels, Map Input and Map To.

TE:

The texture itself is designated by its name here, which you can edit here.

Select an existing texture

Same as for #Empty Channels.

Clear

Clears the texture from the active channel. The texture data still remains and can be added back to the same channel or another channel from the existing texture selection menu

Number of users (number field)

The number of materials that use the texture. You can't create a "Single User" copy here, you have to do that in the Texture buttons (F6).

Auto (car icon)

Automatically generates a (hopefully relevant) name for the texture

Texture Panel with one texture shows the texture with the two new panels. These panels are organized in the sequence in which the texture pipeline is performed:

• in the Map input panel, you choose how the active texture is mapped on the geometry
• in the Map to panel, you choose how the active texture affects the material properties

The channels stack

Each texture channel has its own individual texture mapping. Textures are layered upon each other and executed one after another from top to bottom. This means that for example the second channel overlays on top of the first channel.

(De)activating a channel

By clicking the toggle at the left of the channel you enable or disable the corresponding texture in the stack.

Changing the order of the textures

By selecting a texture and clicking on the Up and Down arrows, you move the selected texture in the channels stack, so to change the overlay order.

Copying and pasting Texture Channels

By adding an existing texture to a channel, you create a link to that texture, but all the mapping options remain as they are. To copy all texture settings, including the contents of the Map Input and Map To panels, you can copy a given texture channel and paste it into another by using the copy and paste buttons.

Copying and Pasting is used when you want to combine two similar textures where each is slightly different from the other. Rather than manually duplicating the properties of one into another just copy and paste.

Copy (Arrow up)

Copies the active texture channel's settings into a temporary buffer.

Paste (Arrow down)

Pastes the copied texture channel information into the active texture channel.