What's the difference between "already taken" and "not available"?
I've been looking up some domain on the "whois" search and found a domain is available. When looking up this domain on Godaddy, it says the domain is "not available". When a domain is taken, it's usually marked as "already taken".
What's the difference between the two statuses and why can't Godaddy gimme my domain?
Without knowing the domain, it can be hard to say. Usually domains listed as not available mean that there is a restriction on the domain name or it is reserved by the domain registry. Sometimes you can look up the domain name on the Registry's website for more information.
It could also be for a domain extension (TLD) that GoDaddy doesn't support.