Line items

Hi, I'm junior PHP developer with no previous experience. I'm task to create the following.
-----One----

Log into the system
On the list page click on the course that is now completed
Click on the “delegate admin” button
Capture the delegate fields a. Delegate count (number) b. Municipality / Org (select from the list) c. A switch for “is billable” d. Amount billed e. Click the plus button to include another line item then start at A for the new line item. Rinse repeat till done
Click save

I'm using twig on the front-end. How to do the above functionality with twig and send it to PHP to save to the database?

I nee something like on the attached screen. I created this one using java-script.