I'm not sure I understand the "ad" (add?) part, as I imagine you weren't solicited or invited as much as you just signed up on your own initiative, but, all the same, welcome!
Make sure you don't ask about the value of the knife, as that is something that requires a paid membership for (as it could potentially be used as a way to find people interested in purchasing something)
You'll find there is a wealth of knowledge here, sometimes lost in a haze of curmudgeonliness. Don't be scared away, though - despite how many sharp pointy things we own, we're harmless and generally good folk.