Each USB port is capable of 5V/2.4A. For comparison, a standard USB port on a computer only delivers 500ma. When a phone is connected to a computer's standard USB drive, it will draw a maximum of 500ma. Many electronics, an iPhone 5 and 5s for instance, are not set up to handle anything more than 1A. You could get a higher amp charger and it won't charge any faster than 1A (interesting enough, an iPhone 6 is set up for 2.1A, but shipped with a 1A USB cable). Handling of the power also depends on the cable length and the internal wire diameter. A long USB cable with small diameter wires can possibly choke on a 2A charger. Having said that most newer cables can handle 2A, and all USB 3.0 cables should be able to handle 2A (you'll your cord is USB 3.0 if there is blue inside the USB port).
USING THE CHARGER
The blue LED lights up to notify you that it's plugged in and ready to charge - basic stuff. If you don't want to see the blue light while driving, you can rotate it to be under your USB cord (see picture below). The charger is small enough that you don't have to be too concerned with it getting in the way. I can be using my phone and the charger still supplies more power than I am using. Keep in mind your results may differ depending on your electronic, USB cable, and the length of USB cable. In other words, the Amperage I might get may not be what you get. Please note that I have NOT left this in the car during the heat of the summer yet. I have lost a few that way, so it's worth mentioning.
Please note that I received this product for free in exchange for my honest, personal evaluation. I hope my review was helpful. If you have questions, please feel free to comment below!