What is a nixie?
A nixie tube is a neon discharge tube with number-shaped electrodes and a mesh cage. The mesh cage is connected to 175 volts DC through a 10k resistor, and one of the ten numbers gets connected to ground to make it glow.
A word of warning: Mishandling the high voltage line can lead to fatal injuries. Replicate any circuit with this display type at your own risk.
Is high voltage necessary to light a nixie?
Yes, no way around it. The neon inside ignites at 175 volts DC, so if you plan on making a nixie tube circuit, do so at your own risk. Never let anyone under 14, over 50, or with a heart condition handle high voltage.
How does one get a number to light in a nixie digitally?
A simple solution would be to use the 74141 IC, or the Russian K155ID1 equivalent. Just connect the grid to 175 volts positive through 10k resistance, the numbers to the appropriate outputs on the IC, and 0 to 5 volt signals to the BCD lines. Then power the IC with 5 volts... you should see a number glow in the tube.
WARNING! Do not touch any connections near the nixie tube while the circuit is live.