Stickers are the newest addition to Kongregate.com! You can collect and upgrade stickers and use them in chat to show off to your friends. You can use stickers in all chats across Kongregate.com.
In the bottom left corner of the chat text box you'll see a new icon:
Clicking on it without any stickers will show you the following box:
Clicking on "Get Stickers" will take you to the sticker marketplace, where you can trade Blocks for sticker packs.
(Related reading: How can I earn Blocks?)
After trading Blocks for stickers, you'll see this:
(These are example stickers and might not be available.)
To find the recently used stickers, you can select the clock icon in the bottom bar. Hovering over the sticker will show a larger view:
Click on a sticker to use it in chat:
Learn about how you can get more stickers here.