Yourself, your learning objectives, your learning experience, etc.
Some topics: Why you would be a good person to recieve the scholarship, what you hope to achieve with the scholarship, etc.
Dont talk too much about how underprivileged you are. Make it a small subsection of the essay. What they wanna hear is plans, goals, and hopefully see some writing talent.
If you know someone who writes really well, it wouldnt hurt to give them a few things you'd like to say and have them write it for you.