CORRECTIONS:

In this post I would like to share videos I was watching when I start to learn English.
...when I started (past tense)

It's clear from his videos that he likes to do so.
...like to do them (the videos)

It's nice remember and rewatch the video one more time.
It's nice to remember (infinitive form)

...the most important in his first video...
(the most important what? Thing? Topic?)

But, I thought,* what if you write a post about why do you learn it ...*
(no need for a comma after "but" in this case, a comma is needed after "thought")
...about why you learn it...

...that series called...
...that series is called...

I like also how he always show nice places and teach...
I also like how he always shows nice places and teaches... (3rd person singular always has "s" or "es", 3rd person singular is equivalent to "he, she, it")