OK. So you've downloaded the latest version of Ubuntu, or even scored yourself an installer CD. Something doesn't go quite right with the install - where do you go next?
You may be able to still use Ubuntu as a live CD, meaning you could use it to access the internet. Or, if you were thinking of trying a dual-boot installation, you could still get on to the net from your existing install.
The first place I look is the Ubuntu forums. They are quite popular, with loads of visitors. Whatever problem you're having, someone is bound to have had something similar. These things are invaluable. As a matter of fact, even though I've visited them for years, and found heaps of solutions, I'm still yet to make a post myself. I just haven't needed to. The same thing happened with the Gentoo Linux forums, back when I used to run that.
As a matter of fact, if you can't find an answer in the Ubuntu forums, try some different ones - like the Debian User Forums. Since Ubuntu is based on Debian, there is a lot of similarity.
Another community I've been a long-time member of is Overclockers Australia. Their forums also provide a wealth of information - the Other Operating Systems forum in particular comes in quite handy.
Back on the Ubuntu site, you could try the Official Ubuntu Documentation. Sometimes though, it can be a bit lacking in detail, or it can be a little dated. This is why I suggest visiting the forums first.
Then there's always Google. Which could be how you found this page...
Another option is to download the free ebook, Getting Started with Ubuntu 10.04, by the Ubuntu Manual Project. Lots of info there in setting it up.