An API (Application Programming Interface) is a way for systems to communicate with each other.
Cryptocurrency exchanges provide this feature as a means for other systems (such as Stacked) to connect and retrieve data as well as perform actions such as placing and canceling orders.
Stacked requires API keys for your exchange trading accounts so you can take advantage of the features available in the platform - including portfolio monitoring (which requires "read" permission) and trading (which require "trading" permission).
When you create API keys for an exchange account, be sure to grant only the permissions that you plan on using with Stacked. Do not re-use these keys anywhere else, or share them with anyone else. You also don't need to store them as you can create new ones if needed.
To learn about the process for setting up your exchange account, click here.