This is the part in the movie where Hiccup's dad is talking to him about how Hiccup would be allowed to do dragon training while he is away. Hiccup doesn't want to kill dragons, instead, he wishes to tame them. He wants to refuse, trains anyway. This shows that Hiccup will try his best to make others happy, but he also needs to make himself happy, too.
This is the part in the movie where Hiccup is doing dragon training, like his dad wanted him to, instead of harming the dragon like he is supposed to, Hiccup decides to approach the dragon and calm it down by Petting it in a calm and gentle way. This scene shows that Hiccup is very kind because he has the heart to not kill an innocent creature.
This is the part where Hiccup rides Toothless. This scene shows that Hiccup is no longer scared of dragons and that he doesn't want to harm them.