Two ways. 1) hit reply, then go back and find other posts you want to quote and reply to those. Each time it will append quotes.You can multi quote?
2) instead of hitting reply, highlight text from a post you want to quote. You don’t have to highlight the whole thing. When you’ve highlighted text, an overlay that says “reply” will show up near the text you highlighted. Click that and it will append the quoted text in the reply box down the page. Keep doing that as many times as you’d like.