I use it quite a bit on my headless enos server to copy files from a USB thumb drive.
Cd to an existing directory where you want to copy the file to
Then mount the USB Thumb drive to /mnt
$ cd ~/username/Temp
$ lsblk -f
$ sudo mount /dev/sda /mnt
$ cp /mnt/somedirectory/somefile .
$ sudo umount /mnt
The . will represent the current working directory for the target directory
Anyway, you can use . to represent the current working directory in various CLI commands.
It it just a shorthand kind of thing that is mostly only useful in a terminal situation.
Also can use … in cd commands
$ cd ..
will move you back one directory towards /
$ cd ../..
will move you back two directories towards /
$ cd ../Temp
will move back one directory then switch to directory Temp from there.
One can also use . as part of the full pathname when executing a file that is not in the $PATH.
As long as you are in the directory containing the app
$ ./somescript
So this will execute somescript in the current working directory.
Pudge
EDIT:
For those who learn best by doing, like myself, here is a follow along tutorial on a few bash commands;