Good luck. It's a bit of a learning curve, but once you get it you can use it for loads of things.
One awkward thing though; Vam uses three main textures for the model (Torso, Limbs, Face), but when you export a model from here or daz it splits them up into loads of material slots, the torso material slot doesn't include the neck, hips, nips etc. even though they are all from the same texture. If you are doing a large design or whole skin texture its best to select all the parts to a texture in edit mode and assign them to new material and create a new image texture for them.
3 new materials to make...
Face texture - (from material slots - Face, Lips, Nostrils)
Torso Texture - (from material slots - Head, Torso, Neck, Hips, Ears.)
Limbs Texture - (from material slots - Hands, Feet, Legs, Forearms, Fingernails, Toenails, Shoulders.)
There are also material slots for the eyes, eyelashes and and mouth. I just select them all and delete them from the model so they don't get in the way when painting on the face.
One that is done you can delete all of the original materials.
Have a go, it's a useful skill to be able to make pretty much anything you can think of. It's how I do almost all of my texture work, even for clothing.
Ask if you need any help.
If you're still struggling, feel free to post the image of your tattoo design and I'll paint it for you when I get a chance. (but I'd rather teach a man to fish.)