proof of "number of conjugacy classes equals number of inequivalent irreducible representation"

Question

There are related discussions:
About the number of inequivalent irreducible representations of a finite group

Relationship between number of conjugacy classes and number of irreducible representations of a group

Estimate the Number of Conjugacy Classes of $G$

I am a beginner of representation theory or algebra. There are many discussions related to the title here; however, just application of it. Actually I will apply this theorem to my study, but I am interested the proof.

Is there any lecture or link that has proof of it? or just the intuition behind this is fine.