An Add-on is a file that can be downloaded into Minecraft Bedrock Edition to change how things, such as entities and blocks, look and act in the game.
*Hover cursor over arrows to cycle through Add-ons*
To install an Add-on, click on the download link provided. The file will either be a .mcpack, which is just one pack, or a .mcaddon, which contains more than one pack. Then click "Open in Minecraft" and it will import into the game!