I came across this list of useful linux commands a while back , Some of them have been very helpful on my quest to learn linux and hope they can help you too.

alias Set and view command aliases.
arch Print machine architecture.
awk Pattern scanning and processing language.
bash Bourne Again SHell.
bg Move process running in foreground to the background.
biff Be notified when mail arrives.
cat Concatenate and print files.
cd Change directory.
chage Change user password expiry information.
chgrp Change group ownership.
chmod Change file permissions.
chown Change file and group owner.
chroot Run command with special root directory.
chsh Change login shell.
clear Clear the terminal screen.
cp Copy files and directories.
crontab Maintain crontab files.
csh C shell.
cut Remove sections from each line of files.
date Print or set the system date and time.
dd Convert and copy a file.
df Print file-system disk space usage.
diff Find differences between files.
dig DNS (Domain Name System) lookup utility.
dmesg Print diagnostic messages from system buffer.
dnsdomainname Show system’s DNS (Domain Name System) domain name.
domainname Show system’s NIS (Network Information System)
du Estimate file space usage.
echo Display a line of text.
env Run a program in a modified environment.
false Exit with a status code indicating failure.
fdisk Disk partition table manipulator.
fg Move process running in background to the foreground.
file Determine file type.
find Search for files in a directory hierarchy.
free Display amount of free and used system memory.
ftp FTP client.
fuser Identify processes using files or sockets.
gcc GNU C and C++ compiler.
grep Print lines matching a given pattern.
groupadd Create a new group.
groupdel Delete a group.
groupmod Modify a group.
groups Print all the groups the user belongs to.
gunzip Uncompress files compressed using Lempel Ziv encoding.
gzip Compress files using Lempel Ziv encoding.
host DNS (Domain Name System) lookup utility.
hostname Show or set system hostname.
id Print real and effective user IDs and group IDs.
ifconfig Configure a network interface.
kill Terminate a process.
ksh Korn shell.
last Show listing of last logged in users.
lastlog Show last login times of accounts.
ln Make links between files.
ls List directory contents.
mail Send and receive mail.
man Format and display manual pages.
mesg Control write access to a terminal.
mkdir Make directories.
more Display file contents one screenful at a time.
mount Mount a file system.
mv Move and rename files and directories.
netstat Print network connections routing tables interface statistics
masquerade connections and multicast memberships.
nice Run a program with modified scheduling priority.
nslookup Query Internet name servers.
passwd Change login and password attributes.
ping Send ICMP ECHO_REQUEST to network hosts.
ps Report process status.
pwd Print name of working directory.
quota Display disk usage and limits.
quotaoff Turn off file-system quotas.
quotaon Turn on file-system quotas.
repquota Summarize quotas for a file system.
rm Remove files or directories.
rmdir Remove empty directories.
route Show or manipulate system routing table.
rpcinfo Report RPC (Remote Procedure Calls) information.
sed Stream Editor.
setquota Set disk quotas.
showmount Show mount information for an NFS (Network File System) server.
shutdown Bring the system down.
sleep Delay for a specified amount of time.
sort Sort lines of text files.
strace Trace system calls and signals.
strings Print printable characters in files.
su Run a shell with substitute user and group IDs.
tail Output the last part of files.
tar Archiving utility.
tcsh C shell with filename completion and command editing.
telnet Telnet client.
tftp TFTP (Trivial File Transfer Protocol) client.
traceroute Print the route that packets take to a destination host.
true Exit with a status code indicating success.
umount Unmount a file system.
uname Print system information.
useradd Create a new user.
userdel Delete user account.
uptime Print how long the system has been running.
vi Text editor.
w Show users that are logged on and what they are doing.
wa ll Send message to every user’s terminal.
whereis Locate the binary
which Show the full path of commands.
who Show users that are logged on.
whoami Print effective user ID.
write Send a message to another user.

Please use man command to find out more details about the command and it’s usage, I hope this helps.