How to Unwrap Models in Blender/Wings3D? [Beginner's question]

Can anyone help with unwrapping models in order to texturize them in Blender or Wings3D? (or some other free modelling program)
I’ve working on something for the TF2 contest and I have the model finished as an STL but how do I unwrap it to texturize it in Photoshop? What’s the easiest program?

Thank you so much!

Should help.