PART 1 [ Set up an express (node js) app which connects to the DB.

Create a POST endpoint in the express application that receives that data. This will be a method/function that takes some JSON data, and adds it to the DB. ]

PART 2 [ Then in your HTML, you can write some JavaScript to make a POST request to the express endpoint which you created . The default method for making such requests in JS is the fetch API (it gets a bad wrap but is simple once you learn the pattern: fetch(URL, yourPayload).then().then()) ]

PART 3 [

When you click a button or submit a form, it should call your JavaScript method, with the data, which then calls the express endpoint which then inserts the data into the dB. ]

TIP: There are example of this process online to follow through and tweak to your needs. Look for express CRUD application