How can I tell this? Well, because there is a lot of backstory. What is backstory you ask? Backstory is the history of your characters. It's what has happened to them prior to the beginning of your story, and every character should have a history, a rich history, but a good writer knows when and how to present this history, and often leaves much of it out of the manuscript.
Here are some ways to present backstory. Let's take a new character, Olivia, she is fifteen-years-old and her brother died last year in a drinking and driving incident. Now how can we tell this to the reader?
Straight-up tell them
Matt had been the most popular boy in school. His best friend, Liam, had dragged him to the party that night. Matt didn't want to go. The two of them got into Liam's VW rabbit, but only Liam came home alive. I always wonder what today would be like if Matt hadn't gotten into that car.
Justin leaned into my ear. "Why don't you and I go somewhere else?"
God, he reeked of stale beer. How could he possibly think this was a turn-on? "No, thanks." I tried to walk away, but he followed me.
"I've got my dad's car." He waved his car keys in front of me while he wobbled from foot to foot. He was wasted.
I snatched the keys from him. "Fine, but I'll drive."
"Okay, sure." He smiled. "Where are we going?"
"To your house," I said as I unlocked his door.
"But my mom is home."
"This isn't a hook-up, Justin. I'm just trying to keep you from killing yourself."
"Shit. Sorry, Olivia. I had forgotten about that."
"Well, I can't. He was my brother, Justin, and now he's gone because he thought it would be a good idea to ride around with a drunk like you. Now get into the car." I shoved my hand through the open door, and he dutifully climbed into the passenger seat.
I pick up the picture of Matt and me taken last last year, when we went apple picking. That was just a week before he died. I remember the funeral. I remember Liam crying into Beth's shoulder, and I remember hating him. Murderer, I thought. If he hadn't been drinking that night, if he hadn't made Matt go with him to that party, I wouldn't be here, looking down at his pasty corpse.
All three scenarios express the same information, but through dialogue we also reveal more about Olivia and introduce a new character, Justin. In the flashback, we see a little of Olivia's personality. There are a million ways for a person to react at their brother's funeral. Olivia chooses hate. What does that say about her?
As you're editing, look for huge chunks of backstory and see if you can't share that information in another way. Whenever I get stuck reading a book, it's always for the same reason, the author is telling not showing, so show more and tell less.