How to create an website/webapp to convert an excel file to csv?

I am curious to know how one can go about creating a website/web application, where users can upload an excel file to the website and get a download link for a csv file which is created/converted from the excel file uploaded by the user?

Here's what I think should happen, please correct me or provide some guidance wherever necessary,
(1) We need a webpage to enable the user to upload the file.
(2) The file needs to be validated if it is the correct format, encoding etc before processing it.
(3) Read the uploaded file and process/convert to csv file (How does one do this? Can Python help?)
(4) Put the output csv file into a separate folder??? (5) Provide user with a link to the csv file.

Can someone provide me with a high level overview of how this application can be developed? What are the available technologies to help in this?

Thank you for your help.

Regards.