Hey Dez,
You seem like you are off to a great start actually!
You know why you want to study Public Health so talk about that reason. elaborate on how you felt when your dad had cancer and how you plan to use what you hope to learn in achieving a long-term goal.
Also, think about what groups you have been a part of and what experiences you have had where you have worked on a team or in a group (possibly use
TH if you are comfortable) and write about how those volunteer experiences have hsaped you and how from those experiences the skills you have gained will contribute to the college.
That is what I would do.
Start out with an intro briefly highlighting what you will be talking about, expand in the next few paragraphs and then conclude by ending with a conclusion that is stating what you want to emphasize from your main body of the essay.\
You can probably find that information on the college's website. The application should be opening in the next month or two I would think.
Hope this helps and is not to confusing!