What you are actually practicing
Keyboard shortcuts are muscle memory once you have them and pure guesswork until you do. The commands are not arbitrary: they follow a system, and once you see the system the unfamiliar ones become predictable.
The conventions come from the design of early text editors, which is why the same handful of keys works in almost every application you will ever open.
How the game works
You are shown a shortcut and four possible actions. Tap the correct one. A wrong pick shows the answer at once.
Easy covers the eight shortcuts used daily. Medium adds the less frequent ones. Hard uses the full list, including the browser-specific commands.
The links worth knowing
Clipboard and editing: Ctrl+C copies, Ctrl+X cuts, Ctrl+V pastes. Ctrl+Z undoes, and in most applications Ctrl+Y redoes, though some use Ctrl+Shift+Z instead. Ctrl+A selects everything in view.
Files and pages: Ctrl+S saves the current file, Ctrl+P prints the current page, and Ctrl+F finds text on the page.
Windows and tabs: Ctrl+T opens a new tab, Ctrl+W closes the current one, and Ctrl+L puts the cursor in the address bar.
Function keys: F5 refreshes the page, F1 opens the help, and F12 opens the developer tools in a browser.
Others: Alt+Tab switches between open windows. Esc cancels the current action. Ctrl+Shift+N opens a new private window in most browsers.
How to get faster
Learn the letters by their editing meaning first. C, X and V are a family: copy, cut, paste, with V chosen because it visually resembles a V-shaped paste mark. Z and Y are undo and redo, and because they sit next to each other on a keyboard they became a pair.
A note on the exceptions
Not every application uses the same keys. Ctrl+Y means redo in most editors but repeat in some text fields. Mac keyboards replace Ctrl with Command for most of these, and use different keys for cut and paste. The conventions are strong, but not absolute.