<command> -h 

The -h flag almost always provides help on a command. Use it!

ls

List the contents of the current directory

cd <directory or full path>

Change to that directory or path

cp <source> <destination>

Copy the source file to the destination

cp -r <source> <destination>

Copy the source directory to the destination directory

mv <source> <destination>

Move the source file to the destination

mkdir <directory name>

Create a new directory

wget <URI>

Download the file at the given URI to the current path

tar -xz -f <file> 

un-gzip and un-tar the given *.tgz or *.tar.gz file

rm <file> 

Delete the file

rm -r <directory>

Delete the directory and all contents

killall <program name>

Kill all running processes of the program

ps

Show running processes

top

Show running processes in a graphical frontend