There are two directions a narrative can go in: linear and non-linear.
For a narrative to follow a linear style means for it to go in the order of Beginning, Middle and End.
So, for a narrative to follow a non-linear style means that you can place the story in whichever order you wish!
Whether you choose for your story to be linear or non-linear is your choice – but try to think what suits your story best.
Would it be more interesting for your big action scene to come first, so you can draw the reader in straight away? Perhaps you would prefer to start at the beginning, so that your readers can understand the characters before anything else happens.
Your story, your decision. Think outside the box – it’s always okay to be different!