How to share folder in Virtualbox with Debian OS Guest

In order to use shared folder functionality few prerequisites need to be met:

• Make sure that Guest Additions are properly installed on the guest OS.
• Users in a guest Ubuntu must be in the group vboxsf to be able to access shares.
• Define a directory on the host that will be used in the virtual machine using the settings dialogue of Virtual Box.
• Do not share personal folders like /home/username or My Documents
• avoid special characters or empty spaces in the path to the shared folder
• use different names for share and mountpoint
• create a mountpoint on the guest OS (best in your HOME directory)