Couldn't help noticing - Tradução em português

Hi every one, I'm here to ask you some help, I was reading a book when I found a not dificult phrase, but I got doubts:

"he couldn't help noticing that there seemed to be a lot of strangely dressed people about"

So, I have these questions:

1) What is meaning of "he couldn't help noticing"? Why "help"?

2)Why is there the word "about" in the end?

Thank you very much.