The Android users will need to get the 2.18.329 version for WhatsApp and iPhone users need to update it to version 2.18.100.
For the Android Beta users, WhatsApp needs to be updated to version 2.18.329 as well.
There is no news on whether this feature is being rolled out to Windows phones.
According to a blog post by WABetainfo the activation of the feature might be slow on iOS while Android phones should see the feature show up with immediate effect.
The user first needs to update their WhatsApp app to the version which supports stickers, then after opening the chat go to the sticker section.
The new sticker option is said to be available on the chat bar on iOS and as on the keyboard in Android.
Once the sticker pack opens you can choose your preferred sticker and click on the send button.
The feature can be seen to work in a similar fashion to Messenger and Facebook stickers. Also, the report mentions that WhatsApp is expected to support not only the Facebook Sticker packs but also might support Sticker packs from various third-party vendors in future.
Today, the following 12 Stickers Packs are being rolled out on WhatsApp for iOS and Android:
Cuppy by Minseung Song, Salty by Alisa Kryzhanovska, Komo by Sanat Rath, Bibimbap Friends by Pete Ellison, Unchi & Rollie by nu1t, Shiba Inu by Aiko Kuninoi, The Maladroits by Cole Ott, Koko by Hanasake Picture Inc., Fearless and Fabulous by Ann Shen, Banana by Jayde Fish, Biscuit by Ghostbot and Hatch by Hatch.
These packs include static stickers which are free. There are also sticker categories through which the user can quickly search a sticker from a specific category.
There is also an official WhatsApp sticker store from where you can manage your stickers and look up all the stickers sent in a specific chat you can check out the Storage Usage section.
WhatsApp is also said to automatically group the stickers to save space just like the Album feature. This is done when the user enters the chat again.
Even the sticker might group themselves, the user can separately choose to star, forward or delete a sticker.
iOS users will also be getting the GIF option in chats. This option will soon be enabled for Android phones as well.