The basics of texturing involve some simple math to map coordinates in a 2D plane to a 3D model. In order to do this, the 2D texture has its own coordinate system in the U and V axis. U is the horizontal axis and V is the vertical axis of your texture, and they both go from 0 to 1 (eg. 0.5,0.5 would be the middle of the texture).
See Create the UV Map
Once you have all your UV's done you "stamp the UV mesh" to a texture file, giving you a template to do your texture files over the top of. Then do the rendering and tangents as described in the forge tools documentation folder and your textures are done. The tangents are done similar to the UV's in the texture editor just using the rotation of polygons or polygon groups and smoothing in the tangent operator.
Use any image editor that can edit the .dds format. This will require the DDS plug-in on most image editors. see Modeling Tools
A particular model can use up to 3 texture sheets using the .DDS format
DXT5 ARGB 8 bpp | interpolated alpha
choose GENERATE MIP MAPS in the mip map generation
See Also: AMDs - The Compressonator for converting DDS files
For example the Kol Battleship uses 3 textures. The primary color texture would be "CapitalTechBattleship-cl.dds". You will also see 2 other textures like "CapitalTechBattleship-nm.dds". This would be the Kols "normal", or "bump map". There is a 3rd texture for the Kol called "CapitalTechBattleship-da.dds". This is the texture that makes all the data lighting fx.
This is the color, or diffuse texture, and one that would show the ships colors as they would normally appear in game. Open the file in Photoshop, or Gimp, and view the "channels". You have your normal red, green, and blue channels. These channels you normally don't touch, However you have a 4th channel, an "alpha" channel.
The alpha channel represents the "Team Colors" channel. This is what surfaces should display team colors of your fleet.
This is the normal, or "bump" map. A greyscale image that simulates raised, and lowered areas on the model with shadows that change depending on the direction of the light source. You can create your own normal maps using the Nvidia dds tools provided with the plug-ins. On a bump map white is a raised area. While black is a lowered, or indented surface.
Channels do not need to be edited individually since it is a greyscale image. The developers duplicate the Red channel and use it as the Alpha channel. If the normal map has no alpha then the model has weird effects in game. Just duplicate the Red channel and rename it to Alpha.
There is also a Normal Map Filter for Gimp and tutorials on YouTube.
This is where things get very interesting. The "da" file means "data". As in your luminosity, or light map, "bloom" ,and reflective surfaces. This is an RGB+ alpha image (red, green, blue, and alpha channels) Each channel represents a certain aspect of the model. You will need to view, and edit each color channel individually, because each color channel has a different effect.
The Red Channel now represents the "Specular Map" of the model. It is how the ship gets that shiny metallic look to it. This is a greyscale image. The lighter areas are more shiny with white being the shiniest while dark is dull areas with black as being no shine at all.
Note: Previous to patch 1.12, and Entrenchment the Red channel was the "Team Colors" map of the model.
The Green Channel is your luminosity or light map. This is what areas of your model that should be "lit up" or, illuminating.
The Blue Channel is your "Reflective" channel. As in "chrome", or mirror like surfaces that will reflect the space around them just like a mirror.
Finally the Alpha Channel. This is identical to a light, or luminosity map. However the lit surfaces will cast a "bloom", or aura effect around it. As with other images the whiter the surface the brighter with white being the brightest. Darker has a dimming effect with black being no effects at all.