You have made a mockup on paper and now you will make a mockup using Polymer. Maybe you want to rethink your design, maybe not. That is your choice. The functionalities do not have to work yet, but you will have to create a response. This is a group assignment, so make sure you all agree on the design of the mockup and divide the components or features amongst yourselves.
The very first step is transforming your paper mockup into seperate Polymer elements. Think in modules, break up everything into the tiniest seperate component possible.
Make a mockup using Polymer components use your previous drawing and create components place it on the screen accordingly
Mockup definition wikipedia: Mockup Definition
Make a number of input fields. This number can also be one.
Create a minimum of one input field using Javascript
The input fields do not truly have to work yet, the input fields only need to give some sort of feedback. This is easily accomplished with an alert. However, if you want to go overboard and add computational fireworks to your mockup, you are welcome to do that.
Create an alert response for every module that requires user interaction
Alert response W3C: Alert response