I think I'm an "overbooked passenger"

Ugh! I'm taking two flights today. Got a seat assignment on the first and not on the second! I'm pretty sure that means I'm an overbooked passenger and now I have to hope for a no-show. I need to do some quick looking on the airline website to see what my rights are so I'll sound intelligent if necessary. Otherwise, no need to appear intelligent. Whew!! ;-)