Just a little of the Rudiments ;)

To manipulate files
List files (List directory of files).
        Type ls to list all files in your current directory.
List all files (long format).
        Type ls -l to list all files with permissions, ownership, length.
List all C source code files (long format).
        Type ls -l *.c to list all filenames that end in .c in long format.
Make sub-directory
        Type mkdir directoryname to make a sub-directory.
Change to another directory
        Type cd directoryname to change to another directory.
Move up one directory level
        Type cd .. to move up to the previous directory.
Print working directory
        Type pwd to display the current directory you are in.
Change to home directory
        Type cd to change to your home directory.
Copy file
        Type cp filename newfilename to copy from one file to another.
Rename file
        Type mv filename newfilename to rename a file.
Move file
        Type mv filename directoryname to move a file between directories.
Remove file
        Type rm filename to remove (erase, delete) a file.
Remove sub-directory
        Type rmdir directoryname to remove (erase, delete) a sub-directory.
Read files one page at a time.
        Type more filename to list a text file one page at a time.
List files one screen at a time.
        Type ls -l | more to list a directory of more than 22 files.

A Basic Commands List
ls
        show directory, in alphabetical order
logout
        logs off system
mkdir
        make a directory
rmdir
        remove directory (rm -r to delete folders with files)
rm
        remove files
cd
        change current directory
man (command)
        shows help on a specific command
talk (user)
        pages user for chat - (user) is a email address
write (user)
        write a user on the local system (control-c to end)

pico (filename)
        easy to use text editor to edit files
pine
        easy to use mailer
more (file)
        views a file, pausing every screen

sz
        send a file (to you) using zmodem
rz
        receive a file (to the UNIX system) using zmodem

telnet (host)
        connect to another Internet site
ftp (host)
        connects to a FTP site
archie (filename)
        search the Archie database for a file on a FTP site
irc
        connect to Internet Relay Chat
lynx
        a textual World Wide Web browser
gopher
        a Gopher database browser
tin, trn
        read Usenet newsgroups

passwd
        change your password
chfn
        change your "Real Name" as seen on finger
chsh
        change the shell you log into

grep
        search for a string in a file
tail
        show the last few lines of a file
who
        shows who is logged into the local system
w
        shows who is logged on and what they're doing
finger (emailaddr)
        shows more information about a user
df
        shows disk space available on the system
du
        shows how much disk space is being used up by folders
chmod
        changes permissions on a file
bc
        a simple calculator

make
        compiles source code
gcc (file.c)
        compiles C source into a file named 'a.out'

gzip
        best compression for UNIX files
zip
        zip for IBM files
tar
        combines multiple files into one or vice-versa
lharc, lzh, lha
        un-archivers, may not be on your system

dos2unix (from) (to)
        strips carriage returns out of dos text files
unix2dos (from) (to)
        adds carriage returns to UNIX text files