The first declaration was by Austria-Hungary on Serbia. Something they wouldn't have done without German support.
Germany declared war on Russia and France.
Germany invaded the neutral country of Belgium in the hope for a quick victory over France. Their invasion was brutal and shocked the (western) world. Although not all stories were true tales of crimes against civilians and acts of barbarism were widespread in the media. The fact that Belgian neutrality was guaranteed by the Germans only made matters worse.
The UK also guaranteed Belgian neutrality and combined with their concerns about German ambitions led to the declaration of war by the UK. Something the Germans didn't expect.
They lost in the end making it hard to spin another narrative. (The narrative would be that due to Germany geographical position they don't have the luxury of other countries. UK has the sea, France has strong natural borders, Russia is vast. Germany has neither of these and is surrounded on all sides. They can't bide their time like the English, defend like the French nor tacticly retreat like the Russians. Quick offensive action was their only way out and if the rights of sovereign neutral nation have to be trampled, tant pis.
They are rightfully seen as the aggressor but that doesn't mean they bear all the guilt. The web of alliances, Jingoism, the Russian mobilisation and 19th century style real-politik played their part as well.