Greetings, @vedantc98, and welcome to the Plone community. We are glad you're here and interested in working with us for your GSoC experience.
You should begin by following the five steps outlined at the top of this post. That is the best route to begin learning about Plone: what it is, how it works, and how to develop for it.
Once you've built a basic Plone website, and worked on some simple issue, you'll want to focus your attention on two packages in particular: Products.membrane and dexterity.membrane. The core of this project involves cleaning up the code for those two packages and merging them. The former package represents the old way of doing things, the latter package is the new way.
You'll want to reach out to @jensens and @mauritsvanrees as well as @agitator, all of whom have experience in this part of the Plone code base and can help you begin to establish an idea of what needs to be done.
Hoping this helps you to get started,
Cris