What is Sentinel Hub
Sentinel Hub is a multi-spectral and multi-temporal big data satellite imagery service, capable of fully automated archiving, real-time processing and distribution of remote sensing data and related EO products. Users can use APIs to retrieve satellite data over their AOI and specific time range from full archives in a matter of seconds.
How to read this documentation
For the new users the collection descriptions (under Data) will probably be the best place to get the information on what you can get from the API. There are some API call examples at the end, which should help the user get their first set of data from the API.