The Facebook Chat Stickers are large sized emoticons and are actually illustrations of different characters. Facebook has also integrated a Stickers Store for users to browse, purchase paid stickers and download them. However, very few folks actually bother to access the store for the free stickers. We used Android's version of Facebook Messenger for this guide and assure you that the iOS version will have the same steps.
Open the Facebook Messenger and compose a new message or select any existing messages to load the chat interface.
From the text and smiley input box, tap on the greyed out smiley icon to access the Stickers.
Select the (basket shaped) store icon to access the Stickers Store.
Browse the free stickers from the New or All Column.
Choose the free sticker you wish to have and tap on it. Then tap on the Download button to add the stickers to your Stickers collection.