Okay, let's take this bit by bit.

The FaceRoom in Poser will let you make simple alterations to the textures for the P5/P6 figures. You can adjust for skin colour, beard growth, etc. That's about all you can do in Poser.

The way to modify textures is to take them into a paint program like Photoshop or PaintShopPro. If you can't afford these, there's a free paint program called Gimp which you can download. Also, there's an improved version called Gimpshop - Google them.

UVMapper won't let you paint anything. All it does is pull a 3d model to pieces and lay those pieces out flat, ready to be painted.

Magnets are a common way to make new morph targets, but they are tricky to use. You can export a body part to a 3d modelling program and morph it in there. Wings3d and Anim8or are simple free modelling programs that you can download. There's also a special Poser morph program called MorphMaster.

Working with Poser, like any artistic tool, takes a lot of time and practise. The people here aren't geniuses, ( okay, some of us are ;-)  ) they've just spent years doing this stuff and getting smart at it. The good news is, everybody here is happy to give advice to anybody who wants to learn.  Check out the tutorials here, and head over to http://drgeep.com/index.html for some very good advice on how to use the basics in Poser.

Good luck, and welcome to the world of Poser!