The flashtubes are part of a teleportation system that had been set up for the Galactic Headquarters Earth Base
The flashtubes can be entered by means of a blue portal that appears on the ground or in midair. Those who use the flashtubes to enter Galactic Headquarters enter a system of tunnels below the ground and slide into the base. During Season Three, Atomic Betty's crew would change into their uniforms mid-slide.
This system has been shown to occasionally malfunction. For example, in "Crimes of Fashion," the tubes had materialized a bear suit over Betty's uniform during her outfit change. In "Queen for a Day," the Bangoons clog the flashtubes' hardware with honey, causing random malfunctions to occur more often than usual.
They also are like slides.
Sparky claims to be the flashtube master.