Question: Well you see I am trying to make a book about my Nana's childhood but from her bother Dennie's perspective I have already talked to him but I find it difficult because how do I start the story like or should it be a diary I am not really sure...But how do you think I should get started?? Answer:
I think you should find the story in the events, and outline them just like any work of fiction.
If you're writing from Dennie's perspective, you're writing the story of how watching his sister influenced him as a kid and helped or misled him in solving his own dilemma.
You have to decide if that's the best perspective to tell the story from. If you write from your Nana's perspective, you're writing the story of how she coped with a dilemma or solved a problem, or didn't.
If you think you can write in the voice of either of these people, that could be quite effective. But it also would be fine to write in 3rd person. You may need to experiment to see which narrative style works best for your story.
I think you should look for the meaning in her life story, the message as it were, so you can select the events that are part of that story and leave out what is irrelevant.
Decide where the story begins, where the pivotal choices, actions, or events took place, and where things reached their conclusion. That will give you a basic structure.
Best of luck.