Welcome to Motobrick!
Before you try starting this moto again, note the orientation of the four-screw cap assembly and remove it. Remove the fuel then see if the tank has debris in it. It it does, clean it with white vinegar, rinse it and put a gallon of clean fuel in it. If it doesn't, put a gallon of clean fuel in it. The next thing to do is assess the battery.
Your moto's battery is discharged. A moto that hasn't been ridden might have lubricating fluids that have thickened presenting more friction to be overcome during starting. A discharged battery might cause the starter contacts to seize. We'll cross that bridge later. Charge the battery at the slowest rate of your charger—a trickle charger won't work. Charging could take 12 hours depending on the rate of charge. Once the battery is charged, reconnect it and try again. Run the starter at five second bursts.
Why the battery connections sparked is anybody's guess; you might have inadvertently switch polarity connecting them. Regardless, do these two tasks then report back. In all likelihood, the previous owner knew as little about how the moto operates, and what it needs to run well as you do, but you'll learn.
Start the moto with a working battery, not a booster.