Hi 
The in-built help is a bit rubbish and out-dated but the official documentation is fairly excellent.Â
http://wiki.documentfoundation.org/Documentation/Publications
http://www.libreoffice.org/get-help/documentation/
The guides on the official page are the same as the ones on the wiki but the wiki has more guides and links to 3rd party documentation too.
The official website only has the guides for 3.3.x branch but the wiki has a load of things that have only recently been added for the 3.4.x branch.
The problem with the in-built help is that 2 teams each thought it was the other team's job to update. The docs team doesn't seem to have permissions or access to the in-built help but even if they did then they are a tiny group and are a bit swamped so they have focused on the guides for now. Anyone that wants to join the docs team is very welcome!
Regards from
Tom