NVTT (Nvidia Texture Tools) is a great tool to create .dds textures.
Depending on which texture maps you have, you'll be using different shaders.
In this example, we have a Diffuse, Normal and Specular texture, so we will be using the normal_spec shader.
Step 2: Applying Your Textures
Go to Sollumz Tools panel, Drawables -> Shader Tools and in the list press CTRL + F to find the normal_spec shader.
Select it and click create shader material with the object selected.
Go to the material tab, find the Sollumz tab and expand the Texture Parameters tab.
Apply each of your textures to each Sampler option.
Enable Embedded for each texture if you do not wish to create a texture dictionary.
Step 3: UV Maps and Vertex Colors
Go to the Data properties tab, and open the Color Attribute tab.
Remove the existing attribute, and click the + to create a new attribute, set the name to Color 1, the domain to Face Corner, the Data Type to Byte Color.
Depending on whether this asset is for an interior or exterior project, set the color to red for exterior and green for interior.
Go to the UV Maps tab, and ensure the UV Map is named UVMap 0, Sollumz will warn you if there are any issues.
Step 4: Creating Your Drawable
Select your mesh object, in the viewport press V, and select Convert to Drawable.
Press V again and select Export RAGE Assets.
Change the export options to Native and Gen8.
Step 5: YTYP Creation
In the Sollumz tools, go to Archetype Definition.
Create a new YTYP with the + button, rename the created ytyp.
Select your Drawable and click Auto-Create From Selected.
Click Export YTYP.
Step 6: Importing Files to CodeWalker
Drag all exported files into our RPF we created.
Once imported, restart CodeWalker.
You can now view the Drawable, all textures should be applied correctly.