Hi guys. I just stared using goodreads and I'm a little confused. Books like "The Davinci Code" and "Silence of the Lambs" are the second in a series. I've never read either of them but I've always thought they were stand alone books. My question is, when Goodreads has something listed as "series title #2" do I have to read the first one (or all of the series) to understand it? And if these books are standalone, how do I differentiate them from actual series (like Harry Potter is labeled the same way).

Any help would be appreciated! I've been searching for books I'd like and googling "good books if I liked _____" has yielded some very good options, but when I look them up on Goodreads it's never the first in the series which genuinely confuses me