Where should oxygen tanks be stored?

It is stored just like any other gas.

It is pumped into the tank...the more that is pumped, the higher the pressure. Then the tank valve is shut and the gas stays in the tank until it is released.

One caution that must be exercised when dealing with pure oxygen is that there can be no pertoleum or explosive products used to lubricate the compressor or any of the piping.

This is because pure oxygen promotes combustion easily and can cause violent explosions and fires.

For an example of this, research the Apollo 1 launchpad fire. NASA used pure oxygen to pressurize the cockpit for the astronauts, but a short in a electronic switch sparked a fire that killed 3 astronauts.