Howto?: Run conversion script on multiple files uploaded in web app; zip and provide to user to download

I currently have a bash script which takes a directory, searches it for all files with typeA extension, converts them, and places them in the same directory in a typeB extension. I am looking to develop a webapp on my server which would:

1. allow people to upload more than one file of the typeA extension


2. run the script on those files


3. zip the resulting files of typeB extension


4. allow the user to download the resulting zip.

I am completely new to webapps and scripting on the web, I have basic knowledge in html css bash scripting etc.

This is for educational purposes so any advise would be great! (this is for my teacher)