Need help regarding an assignment

I have been assigned a fullstack web assignment, the problem statement for which is :

Build a system that would help to create labelled text paragraphs. The system should enable a user to annotate/tag a sentence or a part of a sentence and write “person”/”place”/”organisation”/any text that user feels is correct for that sentence. The tagging method should preferably highlight the tagged text in a yellow color.
The system’s basic UI should preferably contain:

A body where the text to be tagged is loaded
A text box over tagged sentences.
A next button
An export button

The system should give the exported result as a json file which has the text’s filename,the tagged sentences/words with their labels.

I need some hints as to how should I start on this one.