>>96700171) get dark ink in the panel lines
2) wipe away excess with a cloth, paper towel, shirt, whatever. Only the ink in the panel line should remain
That's panel lining in a nutshell, you want either very thin paint or pen/marker ink that wipes away easily. I wouldn't recommend a sharpie, a bit too dark and dry, but most any thin felt tip marker should work for a beginner. They make gundam branded ones but anything off the shelf should work, feel free to experiment with stuff off the dollar store.
Do make sure the surface is smooth, if its sanded rough or matte coated the ink will just smudge, stick and not wipe away.
