A quick introduction to 'Echo'
This is the equivalent of common output commands in most programming language (print or puts statements).
For Example:
echo "Greetings"
This outputs just one word "Greetings" (without the quotation marks).
echo "Greetings $USER, your current working directory is $PWD"
This picks up the values of the environment variables and and displays something like:
Greetings prashantb1984, your current working directory is /home/prashantb1984
The above message, of course, will vary from system to system, depending on the setting of environment variables.
Recommended Resource
A quick but useful tutorial for bash newcomers is here.