An API (Application Programming Interface) is a way for systems to communicate with each other.
Often, these systems require permissions in order to grant access to others to the resources it owns - this is done using API keys.
Exchange API keys can be used to allow other systems (such as Quadency) to conduct transactions on behalf of the user. Quadency requires API keys for your 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 Quadency. 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.