Basic Texture Guides

Basic Modding Starting Kit by McDanceyPantsExtreme
Guide

How to Make an Alpha by Bizu
Guide

How to make a Mask by Bizu
Guide

Specular Map from a Diffuse
Guide

Editing the blue channel/Sheer by Koneko
Guide

Transferring Alphas in Gimp by Koneko
Guide

Diffuse Edits by Solona
Guide

Icon Recolor Quick Guide
Guide

Adjusting levels by decomps by Koneko
Guide

.DDS Exporting
Guide

Thank you to @Lise