Given that the deadline for student applications was about 24 hours away when you wrote your message, I'm guessing that it is likely too late to write a substantive proposal for this year. If I'm wrong, and you get one done, that's terrific.
If i'm not wrong, and you are interested in participating, then take a look at the original post for students interested in GSoC and you'll find some steps at the top that can get you started on the right foot for next year. Plone is great for building websites for schools and student organizations, so you can play with our product for a while, get to know what we do best, and what we need, and be in a position to write an amazing proposal for next year.
We hope to see you around!