Novice - web page to create json file and write to disk [on hold]

Total novice user here, on a very steep learning curve as part of my final year group project at University. I'm looking to create a web page hosted on a pi, that when a user navigates to, they are able to fill out a form (with a mix of free type values and drop downs) and then click submit. The contents of this form is then turned into .json format and the resulting file written to disk on the Pi.

A very easy task in theory, but as a total beginner I've got no idea where to start. Anyone who can provide some tips or point me in the right direction would be grately appreciated.

Thanks in advance Adam