Narrative is a series of connected events. Narrative plot is how events are ordered and interconnected. Narrative story is the chronological succession of events. The structure can change the order of events.
Looping narrative starts with the ending, flashbacks can be used and linear narrative is chronological. For example the play Betrayal is told backwards, as is the musical The Last 5 Years and the movie Momento. Whereas the film Sliding Doors is two stories side by side.
For a play you can set it out in terms of tension and time, but it must have an inciting incident and a climax. The inciting incident it is said has to happen by page 10, for example in Harry Potter the 'You're a wizard Harry" moment.
Act1 set up
Act 2 conflict
Act 3 resolution
or as Charley put it, Dream, Vomit and Sculpt. Dream is when you are planning your story/play in your head. When you write your first draft (vomit) and when you edit it (using the three act structure) this is the sculpting stage. Your first draft will have everything in it, then take things out to sculpt it into one story.
The most important part of a play is knowing when to start writing it. The dreaming part is letting the important bits rise to the surface and if you try to write it too soon, you can kill it.
The point of change or time for the scene/acts are put into 5, 10 or 15 scenes or units of action.
Charley recommended the following books to help on structure: The Secret Life of Plays by Steve Waters, Into the Woods by John Yorke and Story by Robert McKee. It is more common now to not put in stage directions and you stand more chance of having a play commissioned if it is a small cast.
WYPH has a bi-annual open script window where you will be given feedback on your script (details on the website) and next time it will be anonymous submissions. You can sign up for Playwrights One on the website too which is an 8 week course, taking place on a Tuesday evening for 2 hours. Also, Furnace scratch nights take place in the Barbour Studio where 3/4 pieces of work will be presented at the venue but you will have to provide your own actors. Apply when the call outs are on. There are also Summer sublets for 2 weeks in either August or September where you can use the space for rehearsals and this is by application.
Other useful resources are BBC Writers Room, The Bruntwood Prize and The Verity Bargate Award.