For beginners, baking a texture atlas for a 3D model involves three core steps: create a low-poly model (simpler than your detailed high-poly), UV-unwrap it to fit one 2D texture sheet, then transfer high-poly details to this atlas.
Use free, beginner-friendly tools like Blender or Substance Painter. Align your high-poly and low-poly models, then bake key details (normals, ambient occlusion) from the high-poly to the low-poly’s UV atlas—this merges textures into one file, perfect for games or renders.
Start small to build skills: Try a crate (low-poly cube + high-poly details) in Blender. Select the low-poly as active, add the high-poly as a “Bake Target” in Render Properties, and begin with a normal map—this keeps the process simple while you learn.