Channels different outlets you can configure for your store, they are global across the API and depending on what channel you set when sending a request to the API can change the output of the response for things such as Products available, Translations and Categories Available.

For simple online stores, one channel will be enough. By default GetCandy will install a default channel webstore. A default channel exists so if you don't pass a channel to the API when you make a request it will use this record.