'A break' as a meaning of 'opportunity'
I saw someone use 'a break' as a meaning of 'a lucky opportunity', and dictionaries also say so too.
Ex) His break came when the policy unexpectedly changed. (When the policy changed, he could defect from his country easily.)

I am wondering I can say like this:
'Winning a lottery was not the biggest break in my life.'
'Finding this website was a break for improving my English.'
'My second break came when I met her.'

I am not sure if I get the picture.
If I don't, could you explain a little bit, please?

Question

'A break' as a meaning of 'opportunity'
I saw someone use 'a break' as a meaning of 'a lucky opportunity', and dictionaries also say so too.
Ex) His break came when the policy unexpectedly changed. (When the policy changed, he could defect from his country easily.)

I am wondering I can say like this: 
'Winning a lottery was not the biggest break in my life.'
'Finding this website was a break for improving my English.'
'My second break came when I met her.'

I am not sure if I get the picture.
If I don't, could you explain a little bit, please?

Answer

In this context, the word 'break,' is usually accompanied by another word such as an adjective, a superlative etc (as in your first sentence).

We would commonly use "of," as the preposition in that sentence - the biggest break of my life was ...

In your second sentence, I think we'd be more likely to say "it was a real break when it came to improving my English."

Your sentences show that you understand the meaning of 'break,' in this context.