I am a high school student. So,while studying about thermodynamics, I've got a little curious about entropy. As I read, entropy is the rate of change of chaos. So, if the entropy change of a system is $\delta$S and the primary and final entropy is $S1$ and $S2$ , then, $\delta$$S$ = $S2$ - $S1$

Now, come to the mathematical expression of $\delta$S I am really disgusted by the very brief answer of the mathematical expression in my book . It is saying that, in a reversible process , the amount of heat or $\delta$$Qrev$ a system is emitting or producing ,divided by the temperature at which the heat is emitted or produced of $T$ , or $\delta$$Qrev$$/$$T$ is equal to $\delta$$S$.

So, $\delta$$S$ = $\delta$$Qrev$$/$$T$

Ok, so my book doesn't tell how does this equation come , and that is the irritating thing. Also, there is another question regarding this topic, when we are talking about the rate of change of chaos , what is the relation of temperature and heat in here?

Although I know that this is a complex part of physics, I am asking for your help so that I can be able to have a clear idea about the matter. Thank you