I know this is an old thread, but found it while searching for the same answer, so I'll post here for others who may be do the same search.
The wavy line represents one cycle of AC voltage. It represents the polarity shift from positive to negative as AC would be plotted on an oscilliscope or drawn on graph paper.
For comparison, DC is either a horizontal dotted line (when rectified, such as from a power pack) or a horizontal continuous line (as from a battery).
The schematic diagram for a fuse is similar, but has a circle at each end:
As for wiring two tubes to 1 ballast, the tubes are wired in series with each tube having its own starter.
This is from an Australian fluro, so the volts and amps will be different in the U.S., but the watts are the same. Also notice next to AWA it says it can be used for either 1 x 40watt or 2 x 20 watt.
Hope this helps