You may also use an adapter to lower the voltage even more for some devices you use. DC transformers are now available, but they won't replace AC transformers. The reason it is so high is that the electricity travels more effectively over long distances at higher voltages. High voltage lines carry up to 10,000 volts. The transformer near to top of the electrical pole changes the voltage to a safer 110V for your house.
Most people use adapters when they power devices that also use batteries.
An adapter is a transformer that changes the 110V house current to 12V or 9V that is used by the device. It also changes the AC to DC, because the device works on batteries. Changing AC to DC is done by electronic circuitry called a rectifier. Some of the lost AC current is turned into heat. That is one reason your adapters sometimes get warm.