"<span>opinions about the lives of different characters" would be the best answer, because narratives often support this type of analysis. This is not always the case, however. </span>
A backstory for your character is like background information for a character. When you write details about a character before you write your story, you are then able to use these details later on to help you improve your writing. You are able to incorporate their likes, dislikes, childhood, friends, family & more all into what you're writing. Its easier to come up with these earlier on than during your writing.
This is a metaphor that is commonly used in the English language. This simply means that to remove a connection from someone, just like the olden days, you burn the bridge or set it on fire so that no one can cross it again or get to you. To change is to burn the old bridges of the past and head on straight to a journey of the unknown.