Press any key to test it. See the key name, JavaScript code and keyCode, which keys are currently held, and a history of everything you pressed.
If a key does not light up here, your browser is not receiving it, which points to a hardware or driver problem (or a key the operating system intercepts, like some media keys). Nothing is uploaded.
Click the box, then press any key. Each key you press lights up the box and shows its name, so you can quickly check every key on your keyboard works. Keys that never appear are not reaching the browser.
They are the values JavaScript reports for a key. event.key is the character or name ('a', 'Enter'), event.code is the physical key position ('KeyA', 'Enter') regardless of layout, and keyCode is the older numeric code. Developers use this to look them up.
Some keys are intercepted by your operating system or browser before the page sees them (media keys, certain function keys, and shortcuts like Alt+Tab). That is normal and not a fault in the keyboard.
Partly. Hold several keys at once and watch the 'Currently held' list. If keys you are physically holding do not appear, your keyboard may not register that combination, which is a rollover limit.