What are the legalities of using news excerpts in podcasts or blogs?

I am trying to find out what the legalities of using news excerpts on my audio or podcast are? For example on my site BULLMOUTH.com when I talk about industry news; can I quote from a yahoo news story? Do I have to mention where I got it from? Can I talk about the story in an opinion form? I have some confussion on this piece. Thanks for your help a head of time.