You'll need to add lots of tools to your tool box for creating textures. Something like substance painter is the ultimate but also quite pricey. You're going to need something to get the UV maps. for the objects. The cheap way is UV Mapper. http://www.uvmapper.com there's a free version you can use to get started.

UV mapper can export a template you can use to paint textures that will fit your model in any paint and draw program. In the beginning the easiest thing will be to just create simple diffuse color maps. Once you have a diffuse texture map you can drag n' drop the map into Poser material room on the Edit tab. First select the object in the material room with the eye dropper tool. Now drag and drop the image map into the Material Edit tab. Drop it in a blank spot. Drag the output from the Image node to the diffuse input of the root node.

Now you've got a very basic material. Save it to the library. First make sure you have the correct library and folder selected. Click the (+) pus button on the bottom of the library and give your new material a name.

That's the first drop in the ocean. Texturing models is an entire profession in it's self. There are a lot of texture artists here and I'm sure they'll have tons more to add to this.