I googled for plumbers in the Reno area. The results would be like an array. I have entries 1-10 and I can see all of their data at once. It turned out that none of those plumbers had the part I needed.
I called another plumber and asked them if they knew any other business that might have the part. He said no, call company X. I called company X who said to call company Y. This is like a linked list. I have to call or ask each entry in the linked list who is the next company to call.
This continued until one company told me that the part had been recalled and I had to call the company who made the part. This is called a bug and I had to pay to overnight the part. Fortunately for our industry, most bugs can be updated with a patch and not have to ship around a part.