This poem assumes that you've read Dickens' novel Great Expectations and that you already know all about Miss Havisham. Other than that, the toughest part of the poem is its syntax, or sentence structure, which at times can be hard to follow.
Of course, if you haven't read the novel, you might be confused about some of the details and might not know how to tie everything together. But once you catch up on some of the novel's basic plot points (which we've handily provided in "In a Nutshell"), you should be good to go. Don't be intimidated by Miss Havisham. She doesn't want to strangle you, after all (though if you bear a resemblance to her former fiancé, we suggest you tread lightly in her presence).