This is a collection of stories about Celaena as an assassin, and introduces readers to some of the main characters. It is a prequel, the first book in the series starts after Celaena is freed from the mines of Endovier, and this one ends when Celaena is sentenced to work in Endovier. You'll learn that even though Celaena is an assassin, she is a decent person, and you'll get to know Sam, and Lysandra.
It is possible to read this book before reading Throne of Glass, it is possible to read it afterwards. I would recommend people to read this one before Queen of Shadows, because many people from Celaena's past as an assassin come back in that book, reading this will help you understand.
If you read this one before Throne of Glass, you will know what happened before it's revealed in Throne of Glass, but if you read this one after reading Throne of Glass, it might not be as exciting because you already know what will happen.
Although the paperback edition is blue instead of white, it matches with the white paperback editions. and will fit next to those white paperbacks.
The Throne of Glass series in written for teens, and I would not recommend it to younger children because of some violent content, and I would certainly recommend it to high fantasy lovers, as Celaena's world will not disappoint.