All you need to do is to highlight the message and select the reply arrow which will quote the specific message in your response. It’s a pretty cool way to make a direct response on long threads like what you get in some busy groups.
It’s not yet clear which versions of WhatsApp have it. Some but not all users on WhatsApp’s Android Beta program with recent versions (2.16.118; 2.16.119) have it already but some earlier builds (2.16.42) also have access to it.
One thing to note, though, is that if you post a reply to someone’s message and they have a version of WhatsApp without the feature they won’t be able to see the quote it. It’s just another reason to update to the latest version or wait while it makes it way to your phone.
TechZim