In reply to:the meaning of Main Hoon Na is NOT I'm here now.
Hoon is like you have written it in the screen shot and directly translated it stands for "am". Main is of course "I".
So the direct translation of "main hoon" is "I am", but in this sense of the usage it stands for "I am there", which further is the short form for "I am there for you". Written it Hindi it would be, Main tumhare liye hoon. (tumhare liye or aapke liye - for you). Colloquially if you drop the tumhare liye it still means the same thing.
Now for the na: Indians, me including, use na at the end of every sentence.
The direct translation is no. This is a short form for "Nahi". Sometimes if some one asks you a question and you want to reply no. You would say na instead of Nahi.
But using it at the end of a sentence turns it into a qualifier - it would mean "isn't it so?"
As in "You want to go there, no?"
In Indian English we use a lot of na, as in "But you could have come, na? (You could have come, couldn't you?)
The usage of na in Main hoon na would have been clearer if there was a comma after hoon. (Ha! I am not the only one with punctuation problems)
The usage of na in Main hoon na is "I am there for you, no?" Here na is in the sense of "Aren't I?"
So the Main hoon na means "I am there for you, aren't I?"
This whole experience has convinced me that commas are very handy things to have.