Three things nobody ever explained, in about five minutes: what a LAN is, what a WAN is, and why your web browser works perfectly well without the internet.
LAN stands for Local Area Network. “Local” is the whole point: it’s the network inside your building — your office box (the router), and every computer, printer, and phone connected to it, whether they connect by cable or by Wi-Fi. It’s yours. It works whether or not the internet is up, and nothing on it needs the outside world’s permission.
When Rental Books is shared in an office, everything happens on your LAN. One computer holds the books; the others visit it through the office box. No internet, no cloud, no monthly anything — the same way a note passed across the office never goes through the post office.
WAN stands for Wide Area Network — and in everyday life, “the WAN” just means the internet: millions of little LANs, in millions of buildings, all linked together. If the LAN is the rooms inside your building, the WAN is the street outside and every road beyond it.
Why do you care? Because the two get blamed for each other’s problems. If the internet (WAN) goes down, your office sharing (LAN) keeps working — your email stops, your books don’t. And if a computer “can’t reach the books,” the internet is almost never the problem; something inside your own building is. Knowing which world you’re troubleshooting cuts the chase in half.
Here’s the secret most people never get told: Chrome and Edge don’t care where an address is. A browser is a visiting tool. You give it an address; it goes there and brings back the page. Give it an address out on the internet and it brings back a website. Give it an address inside your building — like OFFICE-PC:18723 — and it brings back the sign-in page from the computer in the next room, having never touched the internet at all.
That address is worth reading once, slowly, because it’s just a street address in disguise:
OFFICE-PC — the name of the computer you’re visiting (the building).:18723 — the door number on that computer (the room). Each set of books gets its own door number, so two companies on one computer never get mixed up.That’s the entire mystery of “how can software run in a browser without the internet.” It was never about the internet. It’s about addresses — and some addresses are twenty feet away.
A phone hotspot is your phone pretending to be a tiny router. It creates its own tiny network right there in your pocket. That’s genuinely useful for one laptop in a pinch — and it’s also why a laptop connected to a phone hotspot can’t see the office printer or the office books: it has left the office network and joined the pocket one instead. One computer can only ride one network at a time. Lots of “it just stopped working” stories are exactly this: somebody’s laptop quietly switched roads.
Next steps, depending on your hole: Your Office Network, From Scratch · Sharing the Books in Your Office · All networking pages