The opening of your screenplay should grab the audience’s attention and make them wonder what’s going to happen next. In Act II, this is where your hero starts making things worse.
Why make things worse? Let’s imagine a story where things don’t get worse. Then you don’t have much suspense. What if a story suddenly has things getting better for the hero? Then you have a boring story. You have to make things worse for your hero so the hero can ultimately triumph in the end. By making the hero’s own actions making things worse, that forces the hero to take action to fix his own problems.
Think of Luke in “Star Wars” finding themselves stranded on the Death Star. The easy solution would be to just hide and wait for Obi-wan to shut off the tractor beam so they could escape. Another solution would be for Luke to rescue Princess Leia, run back to the Millennium Falcon, and then escape. What really happens is that after rescuing Princess Leia, Luke has now alerted Darth Vader of her escape and their presence, so now instead of being able to hide and wait to escape, Luke now must run for his life as stormtroopers start hunting him down. That’s making things worse.
In “Die Hard,” Bruce Willis could just hide on the top floor and do nothing. Instead, he pulls the fire alarm trying to call for help, but alerts the terrorists of his existence, making things worse. When he kills a terrorist and sends the body down in the elevator, he’s not only alerted the terrorists that he killed one of them, but that he took the dead terrorist’s machine gun. Now the brother of the dead terrorist swears vengeance on Bruce Willis, making his whole situation much worse.
In “The 40-Year Old Virgin,” the hero’s buddies try to help him get laid. They take him to a bar where he picks up a drunk, attractive woman and goes home with her. Then she throws up all over him, making his situation much worse. Each time his buddies try to help him, their solutions keep him from his true goal, which is to find love.
In “WALL-E,” WALL-E winds up on the giant spaceship containing the human race. Then WALL-E promptly frees a bunch of defective robots while trying to save Eve when he thinks Eve is being dismantled. WALL-E makes his situation worse and Eve confronts him and leads him to an escape pod so he can return back to Earth.
Your hero has to create his own problems and make his situation worse by mistake. So Act I is all about introducing a problem, but Act II is all about the hero struggling to solve that problem and making that problem worse by mistake. Eventually the hero starts making things better near the end and finally triumphs.
By first making the hero’s situation worse, then successfully, you create greater contrast to further highlight the successful victory in the end.