Complex sentence: Stiegler's task is to investigate and explain the interrelation between technics and time, firstly by analysing technics "in" time, that is, by examining theories of technical evolution.
Split into simpler sentences: Stiegler's task is to investigate and explain the interrelation between technics and time. He will proceed firstly by analysing technics "in" time, that is, by examining theories of technical evolution.