In order to use the REST API you need to provide api credentials, more specifically consumer key and consumer secret. There are two ways to supply this important information: HTTP Basic Auth or as a GET parameters.
If you decide to use HTTP Basic Auth, your consumer key and consumer secret are basically your login combination.
If you decide to use GET parameters for auth your consumer key and secret needs to be provided as consumer_key and consumer_secret.
The consumer key and consumer secret can be obtained by creating API Key in the Settings > API Keys section as seen in Figure 1.