There is likely one standard essay for any common app you might apply to and then many colleges ask supplemental essay questions, which are likely available via the mode by which you apply. You'd be able to upload any file once you've written it. Your statement is really one of the only places you have control over on your application. A lot of other information you give (i.e., your grades, test scores, etc) are finite once you attain them. So the essay/statement is where you get to shine. It's important to note that you might hear some talk about writing about some grand life event - it's OK if you don't have something like that to write about. I've read some really good statements about things like.... a dripping ice cream cone; a unicorn sticker that a student had stuck on their wall while growing up; a student's earliest memory. The field is vast. The best statements I've seen are ones that connect emotionally with a reader (whether that be elation, sadness, disappointment, resilience, etc). Also ones where you can really pinpoint what you've learned and how you will take that lesson into your time as a college student.
The Common App provides a list of essay prompts here: https://www.commonapp.org/blog/2019-2020-common-app-essay-prompts
A really great exercise (takes roughly an hour) is to sit down and spend 8 minutes responding to each essay prompt. From there, (take a break first!) go back and choose 2-3 you feel you could expand upon while evoking some sort of emotion from a reader (like I mentioned above). Over a few days, take some time to develop those topics and see which stands out to you the most.
Also - have someone ELSE (or several someones) READ your essay!! Don't be afraid to ask someone you think might be very critical - and keep an open mind to suggestions. It's also helpful just for grammatical tuning purposes.
There is a lot of overlap between the personal statement and common application essay for undergraduate admission. There are some general guidelines to follow in terms of both:
- Write about yourself - Tell a story - Highlight your skills - Explain why you want to study what you want to study
The main difference is that the personal statement will probably be more useful to you in terms of applying to your school of choice when a college essay may come with prompts to chose from. As for submission, Most schools have a link for them on their websites for new students/incoming freshmen.