Essays / Advice needed on writing essays for UK universities [3]

Hi,

I admit that I'm not a good writer but with the help of all the members here, I hope I can be better at writing essays.

I'm a high school student and I'm thinking to continue my education to UK which requires me to write an essay, it is not an undergraduate essay, its an essay for the foundation.

To be honest, I didn't what to write. Should I give a lot of compliment for the university in my essay? Or should I tell a story of my life? Or should I describe about myself and the person I wanted to be after finishing the foundation and undergraduate study at this university? I'm confused.

There are 2 universities that requires me to write essays for the foundation, I was glad by the fact that they gave me the same instructions for both essays. So probably I just need to write one and use them for both universities. Is it okay to use it twice on different university? The university is KCL and UCL.

For KCL Essays there is 4000 characters restriction and 4 paragraph minimum. Meanwhile for UCL, they gave me 2 sheets of paper.
How long you suggest my essay should be? And what should I write?

I have to start small, like this kind of essay, and from there I can learn more and with your help, I can better at writing essays.

Any opinions will be appreciated :)