- Insert toggles between shifting characters after the cursor to the right and deleting the character to the right of the cursor, replacing it with the new character you typed, but not replacing a newline character. While eg. Caps Lock is global, Insert mode is local to the text input that currently has focus - tab or mouse over to a new window and you've lost Insert mode, tab back to the one where you previously set it and you're back to Insert mode.
- Delete is like Backspace, but deletes stuff to the right of the cursor.
- Home, as you discovered, moves browsers to the top of the page. When composing text, it moves the cursor to the start of the line (and vice versa with "End"), CTRL+Home moves to the start of the text entry box.
- Page Up and Page Down shift the cursor by screenfulls of text, typically leaving a couple lines at the top and bottom for context. Note to web developers who are unfamiliar with keyboards: Make sure your fixed/sticky header/footer banners don't hide content when using "Page Up" and "Page Down". Also of note, CTRL+Page Up/Down and CTRL+Tab/CTRL+Shift+Tab shift the window or tab focus within an application, for example to go to the next tab in Chrome or the next file in your IDE.
- Print Screen creates a screenshot. Depending on your setup, this may either go to your Pictures folder, or may go to the clipboard (open an image editor eg. Win+R, mspaint, and CTRL+V to paste). It shares a key with SysRq, which can be accessed with Alt+SysRq+(magic letter), and used to recover from various crash conditions - be careful, if you start hitting letters at random, you'll invoke the bad kind of magic that will shut down your computer.
- Scroll lock was used to stop auto-scrolling an input buffer that was running too fast. Largely neutered in modern OSes, it's still useful in the BIOS when all the hardware initialization messages are scrolling by too fast to read. Sometimes it's also used to toggle keyboard backlighting because it had an LED attached and doesn't have a real function anymore, but depending on the manner in which your OS/hardware neuters this key your keyboard backlighting may not work.
- Pause/Break kills a process like CTRL+C, but sometimes has different specific modes of operation in various debuggers. Access the "break" alternate function with CTRL+Pause.
- Super/Windows key opens the Start menu or search tool. On Macs, it's the Command key and used for lots of keyboard shortcuts. Hyper useful for window management, Super+arrow keys move screens to the left or right half of the monitor, maximize, resize, or minimize them, and Shift+Super+arrow moves them between multiple monitors.
- Num lock toggles between entering numbers with the 10-key section of the keyboard and that section's alternate navigation functions, where 7 is home, 1 is end, 9 is page up, 3 is page down, and 4/8/6/2 are left/up/right/down respectively. Not really important if you've got an inverted-T arrow cluster and Super useful on some dumb 17" laptops that cram in a 10-key section but relegate all these normal navigation keys to arcane random Function invocations on tiny distant buttons crammed into the top of the keyboard if they're present at all. Uniquely, Num Lock is typically remembered across reboots.