Once you've assembled the vacuum system and connected the high voltage power supply, you're ready for a test.
To begin, simply turn on the power supply and vacuum pump, sit back, and enjoy the show!
At first, a continuous red-purple discharge will appear between the anode and cathode. Then, the two colors will begin to separate until there is a distinctly visible dark space between them called the Crookes dark space. After that, striations in the plasma near the cathode will appear and the colors of the discharge will start to become paler. Finally, the striations and dark space will disappear and the entire tube will be filled with a pale blue/white glow. At this point, you have reached cathode ray tube operation.
Here is a brief document that explains some of the plasma-related phenomena visible inside the tube: http://www.madsci.org/posts/archives/feb2001/981758142.Ph.r.html
I've included a picture of the tube operating in cathode ray mode and some pictures of what it looks like during the pump down sequence.