When charging a car battery, you must determine if it needs to be removed or not. In a moment where removing it is necessary, you must first turn off all of the car's electronics, which includes any accessories despite them not being crucial to the engine.
From there, you should remove the negative cable and then remove the positive cable. The former is denoted with a black cable marked with a minus sign while the latter with a plus sign. If your terminals are dirty, it is advised to clean them with a dedicated brush and removing any debris and dirt; this prevents battery acid from leaking as well as reducing the likelihood of malfunctions when everything's connected. Then you can connect the battery to its charger by hooking each cable to a corresponding terminal (positive goes first this time) and then activating the charger at the lowest rate when it's newly used.