WhatsApp is already rolling out the chat pinning feature to everyone. Chat pinning basically lets you pin your favourite chats at the top, so you can always see them without having to scroll all the way down. Unfortunately, you can only pin just 3 chats.
To pin a chat, tap and hold on any chat of choice and you will see an icon that lets you pin. To unpin, tap and hold on the pinned chat and a striked through icon will appear for you to tap.
You must be running on the most updated version of WhatsApp so as to not be left out. Head over to your respective stores (Android/iOS) and make sure it’s up to date.