What is a public ledger?

So, I'm hitting a massive mental wall here, and I really need someone to break this down for me: what is a public ledger?

Seriously.

Last night, I tried mapping out a basic crypto transaction flow for a minor side project (mostly just trying to figure out where my tiny, sad fractional coin actually went after transferring it out of cold storage)—and every single tutorial kept screaming that same exact phrase at me.

But nobody actually bothers explaining what a public ledger is in plain, everyday English.

If I send twenty bucks to my buddy, I know my bank quietly updates a locked-down, proprietary database. Easy enough. But the second we switch over to these permissionless networks, my brain just totally short-circuits. If you were to blindside me right now and ask, "Hey, what is a public ledger?" I'd probably just mumble some embarrassing nonsense about a giant, magical spreadsheet floating around in the sky.

Which I know is hopelessly wrong.

Where I Keep Tripping Up

Can someone clarify the raw mechanics?

• Who exactly forces the ongoing updates onto this thing?
• If every random person on earth can read it, how is my financial privacy actually guarded?
• Where on the physical hardware does this monster data file live?

I grasp the hazy, high-level philosophy of decentralization. I really do. But the literal, nuts-and-bolts operational reality of what a public ledger is continually escapes my grasp.

Connecting the Dots

If I write down a cash exchange on a sticky note and staple it to a busy telephone pole—yeah, that's technically transparent data. Is that fundamentally all we're talking about here? Just a naked list of digital receipts that thousands of uncoordinated laptops blindly agree is accurate?

Or is there some gnarly mathematical barrier stopping malicious trolls from just deleting the entire transaction history overnight?

If a veteran here could just clearly define exactly what is a public ledger without burying me in insufferable developer jargon, I'd seriously owe you a drink.

How does it practically beat a shared Google Sheet?