You ask yourself "How is a tunnel pierced?" and you mean a Flesh Tunnel? Strictly speaking, you can't ask "How is a tunnel pierced?" because it is not pierced like a piercing. A Flesh Tunnel is placed in a stretched piercing canal, which is usually the lobes, i.e. earlobes, but it can also be stretched helix, conch or tragus piercing and in very exotic cases the cheeks or nostrils. We refer to the earlobes when answering "How to pierce a tunnel?".
Piercing or stretching?
Now here are two ways to get a Flesh Tunnel: Option 1 starts with piercing a normal ear hole in the middle of the lobes. "How to pierce a tunnel?" is therefore partially correct, at least as far as the beginning is concerned. This normal ear piercing is now stretched larger step by step. For this purpose, expansion rods and expansion spirals are used, these start from 1.6mm, so you can slowly progress in very small steps. Approximately you could say about 1mm per month. Yes this requires patience and staying power. How is a tunnel stitched? - is a slow affair, but almost painless and gentle, so that cracks and scars are avoided. From a diameter of 10mm you should think carefully about whether you want to stretch further, because up to this point the ear hole will also form back again if you no longer wear flesh tunnels. So up to 10mm plugs you can still turn around and back to your small ear holes and without surgery. How is a tunnel pierced? - means it is stretched and that very slowly and evenly to the desired size. A little tip on "How is a tunnel pierced?" - have the ear hole pierced and not shot with a gun, because when shooting the tissue is much more damaged and you need this tissue to be able to stretch safely.
Or remove it completely?
So what is option two, how do you pierce a tunnel? Option two is something for people who have no patience and are satisfied with a smaller diameter. This is because tissue is removed in this method, which means that it is not possible to stretch larger indefinitely afterwards, as this tissue is missing for this purpose. How is a tunnel stitched? Here it is punched, the method is called dermal punching and the tunnel is punched in about 8mm size with a hollow needle directly from the earlobe. So you get this size immediately, but in return it remains: even without jewelry this hole does not regress, because the tissue is and remains removed. However, the healing usually goes without problems.
How is a tunnel stitched? - is your decision and depends on your financial means, time and care.