Thank you a lot for the advices!

Hi, I am a noob in DSLR, so I need some help. I just bought a lens pen from this site. I observed that it leave (I tried it only on my hand, I was afraid to test it on the lens) that carbon marks other forum members talked about. As I am not the only one seing that, I have to presume this is normal. But now is my question: when I will try to clean the lens wouldn´t the lend get dirty by those residues (that appeared to me kinda greasy, but this might be the effect of being carbon microparticles)? How do I clean those carbon (or what it is) marks I suppose will appear when I use the pen? Shall I use a microfiber after cleaning?
Anyway, I guess this pen is to be used for fingerprints, not for dust, right?
And one more question about the pen: is it to be used also for sensor?
Many thanks