There is a specific dedicated store of sticker packs in iOS 10, but many people ask how to access it?
All you will need is open the Messages app from iMessage App Store and then open the conversation. There is an icon that resembles A at the left of text box, you will need to tap on that. Then tap on four oval icon that is in bottom left side. Then there is a blue + icon which is the sticker store. Go to store then. Then download the desired stickers you want