What you have here is a 'premise'. There's nothing wrong with that. A premise is basically an idea, and all stories start with an idea. A premise for a story can be a few paragraphs long or as brief as a single sentence.
Here's a premise in a single sentence:
A humble farmer is swept up in a quest to a rescue a rebellion leader and helps fight an evil empire.
Sound familiar? You might say Star Wars but this premise is so vague, it could just as easily be set in ancient Egypt, Japan, or Europe. Heck, the farmer could be a girl and the leader doesn't have to be a princess. And if this premise is for animation, the characters don't even need to be humans. In fact, this premise raises many questions. An obvious one is: why would the farmer want to get involved?
What would make this uniquely Star Wars is the details. We know why Luke leaves Tatooine to go on his dangerous quest, but this could easily be a completely different story when we change the details. And that's where you move into a stage called the treatment.
A treatment is a bit longer, sometimes a few paragraphs and rarely more than a couple of pages. It's usually written in the present tense. Just for fun, here's George Lucas' original treatment for Star Wars:
http://www.scifiscripts.com/scripts/Sta ... atment.txt
I say 'just for fun' because this treatment is actually
completely different from the screenplay Lucas wound up writing for Star Wars. But I think it shows how much more a treatment needs to be compared to a simple premise or idea. (This is why 'ideas' by themselves, are not eligible for copyright protections but a unique
interpretation of an idea can be.)
TBH, I think the Star Wars treatment at that link is a bit long. Since this is such a well-known film, a good exercise might be to break down the final version of Star Wars into as few paragraphs as possible--sort of reverse engineering a treatment.
First, you would have to figure out what the barest essentials are to tell Luke's story. Try itemizing those essentials in a numbered list. This list is called 'story beats.' The story beats for Star Wars might go something like this:
1. A renegade Princess Leia is arrested by an evil empire for smuggling secret plans that could aid a rebellion. Before she is captured, she hides the plans in a small robot.
2. The small robot comes into the possession of a humble farming family, an elderly couple and their nephew Luke. The aunt and uncle are executed by the empire but the Luke escapes with the robot.
3. The robot leads Luke to a desert hermit, who reveals to him the story of the princess and the rebellion. Luke decides he needs to help the princess complete her mission. The hermit turns out to be a wizard of sorts and teaches Luke about a magical 'force' that may assist him on his quest.
4. Meanwhile, we learn that Leia is being held prisoner at a moon-sized spaceship called the Death Star. We also learn that the Death Star is the empire's latest weapon, and it is capable of destroying entire planets.
4. Luke's quest leads him to the Death Star, where he rescues Leia. They escape but with the empire in pursuit.
5. Leia brings Luke to a rebel hideaway on a moon, where she explains the plan that will help the rebels defeat the Death Star.
6. As the Death Star approaches the moon and prepares to destroy it, Luke joins the rebels in a spectacular space battle to stop the Death Star. Luke uses the 'force' to destroy the Death Star, and the rebels live to continue their fight for another movie.
Obviously, I left out a lot of characters and stuff that also happens in the movie, but I think this list covers
the most important details that turn our vague idea into 'Star Wars'. Now, write the above story beats as complete paragraphs, and you've got a treatment for a script.
An even better exercise might be to take the original 'farm boy's adventure' premise and make a completely new story out of it.
Anyway, I don't really expect you to do the exercises I described but maybe this will give you some ideas for improving your premise and turning it into a treatment.
Hope this helps.