How to access Windows/Linux Host shared directory from Ubuntu VirtualBox Guest:

1. Create a directory in Windows on any location of your choice.
2. In the VirtualBox go to the settings of the Ubuntu Guest.
3. Under the Shared Folder section add the location of you folder created with full permission.
4. Now start the ubuntu guest, and make sure that you have the latest VirtualBox Guest Additions installed
5. Now add your user to the vboxsf group:

$ sudo usermod -aG vboxsf $(whoami)

6. Logout the user and login again.
7. Now you can access your shared directory in /media/sf_(shared_folder_name).
8. Restart VM