I practiced 'how come' on my YouTube video.

Hi there, I'm Takehiko. Welcome to my blog. I'm so glad to see you again. How's it going? Anyway as always, I'm about to start today's my article & give it a try.
I started recording videos on which I'm practicing English, & also started uploading them on YouTube a little while ago. I'll show you guys one of them today.

On this video, I'm practicing an English idiom 'how come'. I learned this idiom can be used as 'why' or 'I wonder'. Is my understanding of 'how come' correct or not? Besides it, is my English pronunciation acceptable or bad? And, are the examples on the video appropriate or not?
By the way, there's a difference between 'how come' & 'why' when it comes to using them. If I use 'why' I have to use such as 'Why do you...?' or 'Why is it...?' On the other hand, if I use 'how come' I have to use such as 'How come you do...?' or 'How come it is...?'
Well, there're so many idioms in English that it's not easy to learn & memorize all of them. But, it seems to me I frequently hear this idiom, 'how come' in English conversations.
Anyway, that's all this article. How've my article & English today? Thanks a million & I truly appreciate your time for reading. Now, I have to go, bye for now you guys.