On Debian Jessie, VNC Server is installed but not VNC Viewer.
You need to install "Vinagre" (Remote desktop viewer) to be able to use a graphic interface to connect to your Caldera station using a VNC connection.
Open a terminal :
sudo -s [press enter]
apt-get update [press enter]
apt-get install vinagre [press enter] (confirm typing "Y")
Now a new app is installed.
Go to the Debian Menu (circles green logo) > Internet > Remote desktop viewer
To control the current open session : put the targeted IP computer with ":5901" just after.
(Example : 192.168.0.113:5901)
Use the "VNC" protocol.