For adding application launchers, see this more generic question:
I think, you are asking to add a launcher pointing to a location which will be opened with nautilus upon click.
To do so, Follow this:
First create a file naming custom
in your desktop.
Open the file with a text editor (such as gedit or leafpad etc) by double clicking it
Copy the below lines and paste them in the file
[Desktop Entry]
Name=Custom location
Comment=Location
Exec=nautilus /mnt
Icon=nautilus
Terminal=false
Type=Application
StartupNotify=false
Change /mnt
in the line Exec=nautilus /mnt
with a desired location.
You can also change the string in Name=Custom location
line.
Save it by pressing Ctrl + S
Then again rename the file, pressing selecting it and pressing F2. Add a .desktop
at the end of the file.
Copy the file to your desired location. Note, if you delete the file later, the launcher will not work. I assume you copied it in ~/.local/share/applications
folder.
Then select the file and drag and drop it in the Unity launcher.
That's it. A new launcher will be created which will open the desired location when clicked.