That piece of skin at the bottom of the glans is called the frenulum. Almost every male is born with a frenulum. It is normal and it is supposed to be there. The frenulum has a high level of sensation because of its high innervation and serves to limit the rearward travel of the foreskin. The stretching of the frenulum during sexual intercourse helps to trigger ejaculation.
If your foreskin bunches up behind the head when you retract you most likely have a short frenulum (frenulum breve). Test it by pulling back on the foreskin. If the head of your penis bends down when you pull back your foreskin, you have frenulum breve.
You can stretch the frenulum manually just like you do your foreskin. That is the best course of action if the frenulum is too short to permit your foreskin to retract. Search the Internet for:
“How to Fix Phimosis and Tight Foreskins, Solutions That Work”
and you will find the information you need. There also is a minor operation to relieve the frenulum, called frenuloplasty and another called frenectomy. One of these might be necessary, if the stretching does not work. Urologists do this.
Don’t let anyone sell you a circumcision. Circumcision is NOT necessary to treat this