Can I have an explanation on how the gastric bypass surgery is performed?

Gastric Bypass. Make the stomach smaller so you cannot eat as much. Usually by separating the top portion of the stomach from the rest. Bypassing some of the small bowel so you have limited absorption capabilities downstream. A piece of small bowel is then hooked up to the new smaller gastric pouch to allow food to continue downstream. Can be done with open surgery or laparoscopic surgery.
Various ways. There are several techniques. Gastric sleeve is a less invasive band placed on the stomach. Bypass surgery could be a roux-en-y procedure to shrink the size of the stomach and a small bowel bypass to the smaller stomach. Gastric sleeve procedure removes a part of the stomach wall. There are other choices too that you should discuss with your surgeon.
Restrict/malabsob. Laparoscopically, a small upper stomach pouch 15-30 cc is created by stapling and separating from the lower stomach. The small bowel is then divided further down the GI tract and the distal end is connected to the small pouch and the proximal end connected further down to the small bowel. Food then bypasses the lower stomach and 1st part of small bowel. This decreases food intake & absorption.
Small holes & tools. The bypass is done with 5 small holes. Takes about one hour. First, the stomach is divided with tiny titanium staples making a small pouch. Then, the small bowel is divided and the far end is brought up to connect with the pouch with a circular stapler. The other end of the small bowel is attached farther downstream to make a y. Hope that helps.