Such is a word we use to point to a particular kind or degree of something, often to emphasize how extreme or notable it is. When you say “I've never seen such a tall building,” you're highlighting just how remarkably tall it is. When a teacher says “There's no such thing as a stupid question,” she's referring to that specific category (stupid questions) to say it doesn't exist.

The word also helps us connect ideas between sentences. If you write “The storm knocked down trees and flooded streets. Such damage hadn't happened in years,” that such points back to the destruction you just described. It's like an invisible arrow saying “this kind I just mentioned.”

You'll also hear such in the phrase “such as,” which means “for example.” A sentence like “Citrus fruits such as oranges and lemons contain vitamin C” uses such as to introduce specific examples of the category (citrus fruits) being discussed.

Be careful not to confuse such with so. While both words emphasize, they work differently. You might say “It was such a difficult puzzle” or “It was so difficult,” but you wouldn't say “It was so a difficult puzzle.” When such comes before a noun phrase, it usually needs the “a” or “an” in there.