How do I find out the volume of the documents I have saved on my Macbook?

1. Select the folder where your documents are.
2. Do command-I and get a Get Info Window.
3. Get Info will calculate the size of the folder.
4. I can't help but ask: what do you mean by "a full cleaning"?

1. You can do a Get info on All My Files, in the Favorites column in the Finder. I think that will tell you what you want to know.

2. Because Mac is so easy to hack in the first place.

Interesting statement. Do you have any evidence to back it up?

If it's so easy, why don't you go ahead an hack my mac and show me how it's done.

Your Documents should be in /Users/yourname/Documents, unless you put them somewhere else. That is a folder, not a volume.

Also you should read this...

http://www.thesafemac.com/mmg/

The best backup would be a full Time Machine backup, or SuperDuper or CarbonCopy Cloner

You can also use these utilities to back up just the files you want.

EDIT: Note that All My Files draws all files from many different folders.

Movies, Music and Pictures are included in that, so be sure to get your files in there.

As macjack States use Carbon CarbonCopy its great.

To find out used/available space you need to be more specific.

You can calculate storage remaining on mac/users folder/documents folder etc.... blah blah blah the list goes on.

If using the All My Files section

highlight all the files using Cmd+A

then do Option(Alt key)+Cmd+i to get combined info finder pane. Enjoy. 

If you plan to back up your entire user folder, which should be where all that stuff is kept, then just select the user folder and use File -> Get Info. It will take some time to calculate the size. If you don't plan on doing that, and plan to back up those specific things piecemeal, then just look at the size of each and add it all up. Note, though, that hard drives of different sizes have different block sizes, so the size you calculate may not be accurate for the drive you plan on backing up to. For example, a folder full of lots of small files that takes up a total of 1 MB of space could take a lot more or less space on a different drive.

Also, note that a single backup is not really adequate. After you erase the hard drive, you'll only have one copy of all your data, with no backups, leaving you in an extremely vulnerable state until you restore. Many people lose all their data because their backups are screwed up somehow and they don't find out until they erase everything. Make sure to make a minimum of two backups, on two completely separate hard drives.

Finally, regarding the "Macs are easy to hack" comment... that depends. If you have someone malicious who has had unsupervised physical access to your Mac, then you can't be sure of anything. In such a case, wiping the hard drive is the only possible response. After reinstalling, make sure to use FileVault, with a strong password, to encrypt your hard drive, preventing anyone with physical access from being able to modify your system, and be extremely selective about what you restore from your backups.

However, there's no known malware at this time capable of getting past the security built into Mac OS X, unless you help it out by disabling Gatekeeper or installing Java and giving it free reign in your browser. So if you're thinking you got infected with some kind of malware, that's not likely. It's also extremely unlikely, unless you have done something to compromise the security of your Mac, that you have been hacked remotely.