Scooters are fun vehicles to drive around town, but they're typically not used for daily transportation. Because of that, they can sit for long periods of time; and because of that, parts tend to wear down. Batteries discharge naturally over time; so if your scooter has sat for long periods of time, then you'll probably need to charge the battery before you can drive it again.
Park the scooter on a level surface and make sure the kickstand is extended so that the scooter won't roll anywhere. Make sure there's an outlet nearby; that way, you can plug in the charger.
Place the charger next to the scooter and lift up the seat or battery door, depending on your scooter, to access the battery. Clamp the red wire of the battery charger onto the red or positive terminal on the battery, and clamp the black wire from the battery charger onto the black or negative terminal on the battery.
Adjust the settings on the charger for your time schedule. The lower the amperage rating on the charger, the more thorough and solid the charge will be, but the longer it will take. The higher the amperage, the faster it charges, but the battery won't get a very full charge, meaning that it won't last very long.
Plug the battery charger into the wall; or if you don't have enough length to the wall, use the extension cord. Allow the battery to sit and charge for at least an hour; that way, the battery can soak up the charge as much as possible. If you have an automatic charger--meaning it turns off automatically when the battery is full--you can leave the charger on overnight and get the best charge possible.
Unplug the charger and disconnect all of the clamps after a few hours; or if you have an automatic charger, when it says that it's done. Then try starting the scooter. If it doesn't start, then you may need to replace the battery.