WhatsApp has had stickers since last year. The public version of the app offers users its own default sticker packs. The users can also download and send third-party stickers.
The new animated stickers are divided into three parts. The users can send and receive animated stickers, import animated stickers from third-party apps, and download animated stickers from WhatsApp store. The ability to import from third-party apps and WhatsApp store is not activated for beta users yet. Until WhatsApp launches all three parts, the feature is not complete.
If someone with a beta version of the app sends you an animated sticker, it will not load or play for you. You will get to see the normal image. If you are also using the beta version, the stickers would animate as soon as you click on them.
If you want to try animated stickers, you need be part of WhatsApp beta program on Android or iOS. WhatsApp Business will also get this feature.