keyboard
I have a new Apple Keyboard, up until recently pressing the F4 key used to activate Launchpad (Fn keys are set to do as the image on them) but mow it does nothing. I tried the keyboard with another mac and it worked as expected (pressing the F4 activated launchpad). How do I reset the settings on my mac so the F4 key works as I want it to?
PS. I tried going to System Prefs->Keyboard-> reset defaults with no luck.
Almost all of the keyboard shortcuts you've learned on Windows are the same on the Mac. The difference is which modifier key you use to invoke them.
On Windows, shortcuts are typically invoked with the Ctrl modifier key.
On the Mac, you use the 
key, also known as the "command" key. It's in the same physical position as the Alt key on a Windows keyboard, but is nothing like the Alt key.
The Mac has its own Alt key, labeled Opt/Alt. Its primary use is a secondary modifier for keystrokes. Command-Option-S might be "Save As", for example, while Command-S is regular "Save".
The Ctrl key is there on a Mac keyboard, too, but it's hardly ever used for anything.
The relative layouts look something like this:
PC: Ctrl Windows Alt
Mac: Ctrl Opt/Alt
The problem is that you're most likely using a PC keyboard on your Mac. In that specific case, the Opt/Alt and keys are reversed. You can change this in System Preferences, under Keyboard. Truly a huge pain in the rear for switchers. That layout looks like this, instead:
PC keyboard on Mac: Ctrl Opt/Alt
Apple's website has some pretty good hints and tips for Windows switchers. Start here for answers to your specific question about keyboard shortcuts. Then go here and read everything!
Generally the keyboard shortcuts you are used to will rely on the command key. One nice thing about a lot of Mac OS X menus is they will list the shortcut next to the command in question, and you can type the name of the command in the help menu when using the application in question, hover or use the arrow keys to select the menu item options that appear, and see the keyboard shortcuts.
CMD Tab is application switching, CMD C is copy, CMD V is paste, CMD Space is spotlight, swipe up with four fingers is the launcher iirc.
Also if you are in the Finder, you can click help and type shortcuts, there are lists upon lists for various tasks.
Best Answer
On System Prefs->Keyboard-> Keyboard Shortcuts you need to click on Launchpad & Dock on the left, then make sure "Show Launchpad" is checked.