When you sign up for Shopify, you can choose any of their free themes to apply a basic design to your store that you can then customize.
However, there are plenty of premium themes that you can purchase that come with the benefits of:
better design
more customizable
easier to make changes
Some common themes we see students choose are Empire and Out of the Sandbox
High Ticket eCommerce also offers a 'Done for You' theme option where we can design and upload a premium, high converting theme to your store for you.
You can review this option here: https://tally.so/r/mDdKzR