Truly is an adverb that means "in truth" or "really." You would say, "That is truly beautiful" or "It was truly a beautiful wedding."
When you're truly sick, you're really sick. When you're truly sorry, you're sincerely sorry. A truly odd story is extremely strange or bizarre. A truly scary movie is terrifying. This word has to do with things that are actually or absolutely so. It's also used as a closing in letters. Instead of "Sincerely" or "Sincerely yours," many people write, "Yours truly" or "Very truly yours." The idea is: "I really mean this; you can trust me."
