I think we'll get used to the interface quite quickly. I'm struggling a bit and haven't yet worked out how to quote just a section of someone's post - maybe you can't, but more likely I'm just being thick. But it's just different.
The Quote function will quote the entire post and its history.
If you want to quote part of a post, C&P the bit you want and surround it with either two ^ (for italics) or two * (for bold). Or on the web version, there are font format buttons just below the message box, so you can highlight any text you want to format and click the buttons.