This tutorial should get you going with DCS custom livery creation. It covers the basics of the entire process, and by the end you should have a good understanding of how the entire process works.
Feel free to hit me up on Discord should you have any questions.
https://discord.gg/fGuaMr2Asg
DCS: https://www.digitalcombatsimulator.com
Notepad ++: https://notepad-plus-plus.org/
Nvidia Texture Tools: https://developer.nvidia.com/nvidia-texture-tools-exporter
Model Viewer Tips and Tricks: https://forum.dcs.world/topic/229796-model-viewer-tips-tricks/
0:00 Introduction
1:09 Getting Set Up
7:41 Templates & Textures
10:25 Model Viewer
14:38 Arguments
15:56 Attached Objects