The iMac
There is no apple key on a newer iMac.
Yes, with the built in application Garage Band.
The iMac is an Apple computer.
The Apple iMac is a computer and its purpose is to compute.
One can read Apple iMac reviews online at various websites. One can read Apple iMac reviews online at websites such as CNET, TechRadar, and Computerworld.
You do not make the iMac, Apple does.
If you are downloading it from the Apple App Store you must create an Apple ID there.
The Apple iMac comes with iChat Instant Messaging software. You can download other IM software such as Microsoft's Messenger or Adium (See links below) which will connect to many IM services.
To play movies on your iMac, you can use the built-in Apple TV app, which supports various formats and streaming services. Additionally, you can download VLC Media Player, a versatile application that handles a wide range of video formats. Other options include QuickTime Player for standard formats and DVD Player if you're using physical media.
I do not have a 24" iMac. I have a 20" iMac. Apple no longer sells the 24" iMac. If you will click the Apple logo on the top left of your screen and then click About This Mac then More Info you can find the answer.
You can't, it's only available on iMac (apple product, you probably cannot afford it if you have a PC)