Ok...this one is fairly easy to explain. Since you are using a simplified version of a classic literature story, you are reading/using the same type of materials my 7 yr. old son is using for his English Grammar and literature.
These are two seperate sentences, and I'm not sure they came from the same paragraph, so I'm going to address them simply as sentences.
Sentence 1: "pushed open a door". Someone is standing on the outside of a building, they push on the door and it opens. Thus "pushed open a door" that tells you how the door was opened.
Sentence 2: "threw open a door". This one is much the same as sentence one, except that there is more expression in it. It is still stating how the door was opened. But, you can tell that there is more force with opening this door. For some reason, the person opening the door was in a hurry to do something, I'm assuming escape danger. Thus, in their hurry, they quickly opened the door and went inside.
But, both sentences tell you how a door was opened. There are many words/phrases used in English literature like the two you mentioned. They are ways the author uses to draw people into the stories.
I hope this helps.