Green Arrow isn't typically portrayed as an asshole. He's often a hero with a strong sense of justice, but like any character, he has his flaws and moments of difficult choices.
Yes, it can be. It often gives enough background within the story so that new readers can follow along. They'll quickly get a sense of who Green Arrow is and what he stands for.
The origin of Green Arrow lies in Oliver Queen's time on the island. He was basically a rich guy before. But on the island, he became a fighter. He learned how to use a bow and arrow really well. And when he came back, he used those skills to fight bad guys in his city.
Green Arrow's back story involves him being a wealthy playboy named Oliver Queen who survives a shipwreck and develops his archery skills and a sense of justice on a deserted island.
Green Arrow's training in the comics was a complex process. It wasn't just one person or event. His own perseverance, along with learning from various challenges and encounters, shaped him into the skilled hero we know.