Creating and Labeling time series (features)

I am trying to carry out crop type identification using optical remotely sensed data of Sentinel-2A. I am new to both fields (remote sensing and machine learning) and I want to use time series (NDVI, NDWI…) as my input data (training), and I also have a vector shapefile as my labels.

How can I create these data time series?

I am able to create an NDVI map (per raster image/date), but I was not successful with creating a time series per pixel using SNAP. (this is a pixel-based classification)