My name is Marjan and I study in 9th grade.
If your choice of college accepts the Common App or Coalition App, the answer to your question is, yes, you can send in the main one to all. Both applications have a designated space for you to insert your essay that all colleges you apply to will see along with the other information of your application.
Most colleges have writing supplements. This means that in addition to your main essay, the college provides specific prompts that they would like you to answer. Your response to these prompts goes directly and only to that specific college.
I encourage you to explore your college's undergraduate websites. In doing so you can find which kind of applications they accept and you will get an idea of what their writing supplements will look like. It is also a good idea for you to get familiar with both the Common and Coalition application. A quick YouTube search can pop up a vast amount of videos that can explain the two and their differences!
You can submit the same essay for every school, unless your essay is written specifically for a certain school, then I would recommend writing another.
To keep this community safe and supportive:
If you use the common app or coalition they will have a personal essay that gets sent to all schools that require it. Most schools however have a supplemental essay(s) that are specific to that school, so aside from the personal essay you will need to write separate, often, shorter essays. Schools that usually don't accept either of those apps are state schools which have their own application portal.