How does gyroscope work?

Well, I am not so sure how gyroscope in exact details but I can tell you some important fact about gyros.

Gyro basically gives you angular velocity.

Let’s say you have velocity how do you find displacement? You integrate velocity and you will find displacement. Here we have the same story, we have to integrate our gyros output to find angle of headings.

There is a problem with gyros, no matter how accurate they are but they will drift. Imagine a car is sliding; the wheels are not moving so your velocity is zero but you have displacement. Same thing happens for gyros over time so they are not reliable source for reading angles that we need. The other issue is that integrating is not so accurate itself as well. How we integrate in digital world is different from what we learnt in schools. What happens is that we have to measure time interval and multiply that to your sensor reading, which gives us the area under the curve however it is not so accurate. As you can see in picture the gray parts are extra or less measured values that in long term will cause a huge error.

  So errors come in gyros reading from two factors and therefore they are not reliable to be used alone.

  These are the reasons that we can't use gyros alone.

This post needs to be better but for now this is enough :)