What you're describing as "the camera stuck to them" is one of the fundamental elements of writing, the narrative point of view – commonly abbreviated in writing circles as PoV or POV. In the scene you've described, you've adopted a third-person PoV: "his eyes peeped through the gap".
In some writing pieces, the PoV remains locked on the protagonist throughout the story: the reader only ever learns what the protagonist experiences. There's nothing wrong with this approach but it can be quite limiting for both writer and reader; on the other hand, it can be quite realistic (very much like they're wearing a headcam!).
There's also the subjective/objective axis to the PoV. Is the description purely observational, or does the author reveal what the character is thinking or how they're feeling? Here's how your excerpt might look if you added the subjective element:
He leaned against the heavy door, his cheeks resting on its cold, smooth metallic surface, and his eyes peeped through the gap in the doorframe. His heart skipped a beat: that was <PERSON> in the creature's jaws. How did <PERSON> get there before him?
If it was purely the "camera" perspective, the reader couldn't know what the character's heart is doing. And the final sentence is an example of free indirect speech, in which the reader hears the character's thoughts.
Probably the most common third-person narrative is the omniscient PoV, where the reader is given an overarching perspective that's not limited to the one character. This is not only useful for the reader to be able to know things that are hidden from the protagonist, but it also makes it much easier for the writer to describe what's going on. The transition is quite simple to achieve, either by describing the scene from a perspective that the previous character hasn't (at that point) got access to, or by shifting the PoV directly to another character. For example:
He leaned against the heavy door, his cheeks resting on its cold, smooth metallic surface.
Inside the room, the creature effortlessly threw <PERSON> into the corner, and turned to face <PERSON>.
[The protagonist] peeped through the gap in the doorframe, just as the creature seized <PERSON> in its jaws. His heart skipped a beat. 624
How did <PERSON> get there before him?
You see how the middle paragraph has shifted the "camera" to inside the room? You could do this even if the room was devoid of characters: it's simply the anonymous narrator (the author) describing a location.
A more direct way to change PoV is to view things from another character's perspective. This can be as easy as making the other character the subject of the next paragraph. Here's how such a transition might look:
He leaned against the heavy door, his cheeks resting on its cold, smooth metallic surface, and his eyes peeped through the gap in the doorframe.
Inside the room, the creature effortlessly threw <PERSON> into the corner, and turned to face <PERSON>. It could taste <PERSON>'s bravery already, before it had even opened its jaws. Such hopeless defiance. There was the pleasing sound of bones cracking – and another sound, unexpected, from outside the room. The creature swung round, its yellow eyes fixed on the door.
[The protagonist] didn't stop to think. He put his shoulder to the door and pushed with all his weight. It silently, massively, opened. With a roar, he leapt...
Which PoV works best? What's the best way to transition to a different scene or even to a different PoV? There's no definitive answer: you'll have to try different approaches yourself. But the two best pieces of advice I can give are:
* read as much as you can, but now with a writer's eyes: take note of the craft of the author, be aware of PoV, free indirect speech, transitions, dialogue tags, descriptiveness, etc
* write as much as you can! Get your first draft written – don't worry too much if it's a bit messy – then go back and edit, then edit again (and again, etc).
Good luck! 624