Answer:
Through layer upon layer upon layer upon layer ... so on and so on ... of abstraction.
I'll do my best to give some layers.
At one of the lowest levels is electrical components such as resistors capacitors etc.
Put a couple of them together and you create a circuit, throw in some logic gates (AND, OR, XOR etc) and you have some logic handling.
If you arrange this logic gates into some basic configurations you can make circuits capable of math, memory addressing and other advanced tasks.
Put all these peices together with some more advanced connections (Buses etc) and you get a CPU. (You can repeat for other peices for hardware too)
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This CPU is capable of executing some basic instructions called Machine Language, this is basically some numbers that stand for certain memory positions and calculations and logic jumps.
Then to make things easier for people the Assembly language was invented, this assigned some simple words to those machine code numbers and added some automated help (registers etc).
Next comes some basic system calls. Assembly code written that controls your hardware.
Those system calls combined with some other nicities such as memory management, and you get the operating system (OS). (Windows is essentially just this with some pretty windows ... hence the name)
Although assembly is already a step up its still not enough. Eventually other programming languages were invented to make programming easier. Those languages take the code and translate it into machine code.
Using these programming languages programmers can create the programs you use.
Obviously this isn't 100% complete, I missed libraries and device drivers and all that lovely stuff, but the above should give you the general idea of how computers are really just layers and layers of things built one on top of the other to what you use to get your answers.