Need help with the beginning.

I am writing a story, and I have a plot and parts of the story, but I am having trouble thinking of a beginning, like Chapter 1.

Plot:
Aria Glass is a demon hunter, along with her friends who are like family, Jared and Toby Heller. When Aria find out she is a Healer of heaven and that she is the key to stopping the Demon War that is about to submerge from Hell. With the help of a few rebelled Healers and one hell of a determination to do it her way Aria and her friends must stop the army's from coming to earth and fight the corrupted Healers from using Aria for something worse.
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Now I want to begin it after she had met the Healers and found out she is Half healer, but I'm not sure how. Please Help! I'll Give You A Prop!!