I would strongly recommend not using PSP. I started out using PSP to do the texture work on my first few models. The biggest issue is to get them to a printable standard required multiple conversions of the files which in turn resulted in serious degradation in the image quality.
I now use Blender to create the model designs which has an export to paper model option. If you are feeling creative you can also use Blender to texture and render the model you are working on but I could never get my head round it so now use Inkscape for all texturing work.
The results are miles better than anything I could produce using PSP and is actually far easier as it doesn't require files to be constantly converted.
There are countless Youtube videos showing you how to use Blender to build models of varying complexity.
E.g current model I am working on of the MCRN Scirroco
Once you have the model built in blender use the export paper model option and export it as an .SVG file
You can then directly open the file inside Inkscape and start adding textures and details to the model before either printing directly or exporting as a .PDF file
One side of the model, exported and textured
Again a quick search of Youtube will bring up countless videos of how to use Inkscape. If you're used to PSP it will take a bit of getting used to but a combination of trial and error and Youtube videos will guide you in the right direction.
Any questions feel free to ask.