I would like to calculate Strahler's and other stream hierarchy from my input raster but I am not sure how.
This manual suggests tat I should use
r.stream.order command, however in version 7.0.2 "order" is not a recognized command.
Not sure how you are accessing GRASS, but the documentation reads to me like this is an Addon. I just went to the command line typed "g.extension" and a window popped up that I linked to the source page (https://svn.osgeo.org/grass/grass-addons/grass7/raster/) and put in the addon name (r.stream.order)... and it did its thing... hopefully that does it for you :)