You don't need documentation for Mandrake Linux. Any Linux documentation is fine, and some Unix documentation is fine.
You may be surprised to learn that you already have thousands of pages of manuals. On your computer. If you want to read about a certain command (when using the command line) enter man <command>. These are the 'man pages.' Unlike Microsoft help files, they are informative, logical, thorough, and helpful. This resource offers nothing for what you want to do in your graphical user interface; it's command-line only.
www.tldp.org aspires to be the documentation site. The learning curve is steep, but you will learn much by reading the GUIDES and HOWTOS at this site. Linux is a fun, powerful system, but as a newbie you will hit roadblocks. Try to look on them as a learning experience, not a chore. Once you gain minimal competence you can run your computer nonstop with almost no administrative work. Graphical applications are pretty self-explanatory, so don't read about them; just use them.
Great books are Running Linux (mentioned above), Linux Desktop Reference (by O'Reilly publishers), and Unix Unleashed. This will teach you how to use the command line.
Whenever you have a particular question, head first to
www.google.com/groups. Enter search terms + linux. Everything you're going through has been discussed for years on Usenet.
If you can't find the answer to your particular question at tldp.org OR google groups, then post a question on usenet. This forum is nice, but there's really no traffic. Usenet questions get answered immediately IF they are well-formed, specific questions.
Welcome to the world of Linux! Remember that Linux is your operating system; Mandrake is merely your distribution. All Linux distributions use the same command line interface(s) and run the same software (more or less). What Mandrake gives you is Mandrake Control Center, RPMDrake (software installer) urpmi (another software installer which is awesome!), etc. So any general question you have is most likely NOT Mandrake specific. *But* any question *may* have a distro specific answer, so always identify your distribution when asking for help.
I can't overemphasize how much you can learn at
www.google.com/groups, though you must seperate the wheat from the chaff.
When it comes to administering your system, I highly recommend using Webmin. This is a web-based GUI for administering basically anything you could want to do (setup firewall rules, run a mail server, run a webserver, set up a network). It is on your installation media; probably already installed. To login to Webmin you open a web browser and enter the URL: yourhostname:10000.
As a newbie I monitored (daily) the usenet group alt.os.linux.mandrake, and I learned a lot. Other good ones are comp.os.linux.hardware, comp.os.linux.networking,comp.os.linux.security,comp.os.linux.setup, etc. Again, don't restrict your troubleshooting queries to websites like this; use USENET.
Another helpful resource is the #linuxhelp channel on the undernet IRC server. Check that out, but have a thick skin. Ask well formed questions and be happy if someone answers it straight away. (This happens often.) If you are ignored, or someone is rude, shrug it off. Come back later, don't repeat yourself over and over. Here are their rules:
www.getlinuxhelp.org/rules.php .
Here is a guide to asking good questions about Linux. Remember, real Linux gurus are hackers. Hackers only give good answers to good questions. Don't ask 'does anyone know how to install Java?' Yes, they do. Question answered. Neither should you ask 'Java won't install, what's wrong?' Too vague, you won't get a response. Ask 'I'm running mandrake 9.1. I downloaded the java software but can't get the install to work. Here's the step where it failed, and here's the error message I received.' Then they'll help you immediately, with a smile.
Have fun.