Each user has a unique API key.
You will receive it after logging in to your account and going to the API page.
Every request must specify an API key (with the key parameter).
For document request use the access_token query parameter like this
?access_token=[your-api-key]
For search request use the access_token query parameter like this
&access_token=[your-api-key]
You can generate a new access key on the API page.