How to save ePub in Calibre

[Sandfly]

I just joined Mobileread. So I do not know whether I should make my first post here or not. Anyway, I am making this as my first post. I have a question: I am using Calibre to read an ePub book. During the reading, I made some highlights and comments. I did not know how to save the highlights and comments (there was no way I can save). Later I read the same parts again. All of my highlights and comments had gone! Could anyone tell me how to save those highlights and comments. Thanks.