Car battery chargers come in all shapes, sizes, price ranges and options. Reading the information that the switches and gauges are telling you once it's hooked up to a battery is generally the same no matter what kind of charger you have. You get what you pay for in life, so the more elaborate the charger, the more expensive it will be, and the more options you'll have with it.
Hook the red positive clamp to the positive battery terminal (in or out of the car) without the battery charger being plugged into an outlet or the power button turned on. Some battery chargers do not have a power button and automatically turn on when plugged in. Hook the negative clamp to the negative battery terminal.
Read all the other switches before powering up the charger for the correct options. Most chargers have switch options for amp settings and battery types. Some more elaborate chargers may offer different volt settings. For a car battery, you need to switch to conventional battery or non-deep-cycle battery. You want to switch the volt setting (some chargers automatically come equipped with only a 12-volt charging option, as most car batteries are 12 volt) to 12 volts. Last, the amp setting option depends on how quickly or slowly you want to charge the battery. The lower the amperage, the longer the charge will take; the higher the setting, the less time the charge will take. On some chargers, there may also even be a high or "start" option, and this can be used to jump-start your car battery using the charger. Place the amp setting to accommodate your desired task with the battery.
Plug the battery charger in, and or turn on the power button. In some cases, turning a timer dial will power up the charger after it's been plugged in. This timer can be set for any amount of time you wish to charge the battery and will automatically power down the charger when the time expires.
Read the charging gauge of the battery charger to determine what life is left for charge in the battery. This gauge may differ slightly depending on models of chargers, but the information is relatively the same. It will show how much life is in the battery and, in some applications, how much of a charge percentage the battery needs. In most battery chargers, there will be a power light indicating that there is power to the charger, and there may also be a "full charge" indicator light that would alert you that the battery has obtained a full charge and is finished. With some lower-end models, you may have to read the gauge and wait for the "100% charge" or similar indicator.
Disengage the battery charger clamps when you're done with the battery but only after you have powered down the battery charger. Batteries contain volatile acids that create flammable gases and, in some rare occurrences, can ignite and explode if a spark is present when disengaging the clamps from the battery terminals. By powering down the charger (whether you turn the power off, turn the timer to zero or unplug the charger from the electrical socket first), you will eliminate this risk.