There are positive and negative posts under the hood for connection of booster cables/charger - the positive post is on the firewall, offset slightly to the drivers side. The negative post is on the fenderwall, about half way down on the driver's side. It's shown in the owner's manual as well.
You'll get a far better connection using those posts with alligator clips than you will with the notoriously finicky and unreliable connection you'll have using the cigarette lighter in the car. You'll get as good a connection as possible if you hook up the supplied pigtail connector permanently to the underhood post wiring, and leave the pigtail attached for quick connects/disconnects.
You don't need to be concerned with fire or overcharging - these are 'intelligent' chargers that are designed to maintain a battery while connected for months at a time.