As you might know Google has a history of making and then killing the messaging apps and couldn't settle on one. They've made a smooth move with RCS also known as rich communication services and everyone is hoping it doesn't end up in the Google graveyard as well. RCS is a communication protocol rather than an application and can be said as the upgraded version of dated SMS to include WhatsApp or iMessage like features in it. Google is trying to replace old SMS with updated chat features that seem more modern. Messages can be sent through mobile data or WiFi using the RCS protocol.
This is not a single person/party thing, Google has tried to get device manufacturers and carriers to implement these RCS features to which some have completed the transition while most are still lagging. Google implemented RCS support in Google Messages which could setup RCS chat features if the carrier had it implemented. This roll-out has been taking like forever on carriers' side that is why Google has taken some control in their hand to give users the feeling of what the RCS features will look like and how they will work by providing the RCS chat feature through their servers until support from carriers. Recently they introduced RCS in Italy and Singapore and along with that people in Pakistan also started to get pop-ups in their messages app to get these chat features.
How to get these chat features?
You need to install Google Messages and Carrier services from the play store (sorry to iPhone users) if you don't have already. Click on following links
Google Messages
Carrier Services
If you already have Google Messages and Carrier Services installed but didn't get the RCS chat features yet then you'll need to wait. You'll get the popup for availing the RCS features.
If you've been waiting and didn't get the popup asking for RCS chat features, you can clear the storage of Messages and Carrier services. A couple of my friends did get the popup but it wasn't reflecting in the settings and some didn't even get it at all, they had to clear storage for both apps before it worked.
You may or may not get above shown popup confirming RCS has been successfully set up and is running.
After everything is set up successfully, you might wanna have a look at some settings available under chat features.