Welcome to LQ!
Welcome to the RPi (I love mine).
Some good articles for newbies to linux and the RPi can be found at http://www.themagpi.com/
Otherwise, just "explore". I kept breaking linux in my early days, but I learned a lot that way, so keep backups. I found it useful to keep notes about why and how to set things up. It'll be useful when you have to do something again and you say "I did this before, but it was 5 months ago, now just what was that magic command?"
[EDIT] I forgot about apropos
. Most useful. In a terminal type
pi@rpi:~$ apropos directory
alphasort (3) - scan a directory for matching entries
basename (1) - strip directory and suffix from filenames
bf_compact (1) - shell script to compact a bogofilter directory
bf_compact-bdb (1) - shell script to compact a bogofilter directory
bf_copy (1) - shell script to copy a bogofilter working directory
bf_copy-bdb (1) - shell script to copy a bogofilter working directory
bf_tar (1) - shell script to write a tar file of a bogofilter directory to stdout
bf_tar-bdb (1) - shell script to write a tar file of a bogofilter directory to stdout
bindtextdomain (3) - set directory containing message catalogs
chacl (1) - change the access control list of a file or directory
chdir (2) - change working directory
chroot (2) - change root directory
ls (1) - list directory contents
Then, if 'list directory contents' is what you are interested in you can do man ls
to read the manual for ls
How to use man? man man
Above all, have fun.