Q:

What does "tail -f " do?

I don't understand the function of the option -f added to the tail command.
I know that tail views the "last" part of a file. The manual says that

-f outputs appended data as the file grows

But I don't really understand what that means. I know the meaning of each word in the previous quotation, but I don't understand the meaning of the whole sentence.

A:

It means tail -f command will wait for new strings in the file and show these strings dynamically. This command useful for observing log files .
For example try, tail -f /var/log/messages.

A:

You can think of -f as "follow".  When -f is added to tail, the command will not exit but waits to see if more is added to the file; that additional text will be printed by tail.  You normally kill a tail -f with ^c.
It is often used with log files that that are being written by daemons or a background user process. 
tail -f /var/log/syslog

A:

If you have an active log file,program is running while writing info to log file.
you can open the log with tail -f so the log is being displayed "live".
tail -f /var/log/logfile is like constanly doing tail /var/log/logfile

