The Process API is the most commonly-used API in Sentinel Hub as it provides data from satellite imagery: as an image, as source data, or as simple-band combinations of algorithms such as NDVI, LAI, etc.
Even though satellite imagery data are often distributed in "tiles", we do not want users to be limited to these. Tiles are an artificially introduced entity to make data distribution easier to handle. However, users should not have to care about whether their AOI is on one tile or another, or perhaps on the border of two tiles. This is why Sentinel Hub API hides this complexity and simply makes the data available over chosen area of interest and temporal period of interest. Tiles are therefore automatically stitched together based on defined parameters (AOI, time period, cloud coverage, priority, etc., depending on the data type).
We have prepared a process API webinar to help you get started.