I am proficient in Bash and a beginner in Python (I have some experience with Flask and Requests).
I wrote a Bash script which asks for some input (four strings) and creates a configuration file based on that input. That's good for me, but I would like to convert it to a (no frills) web interface.  I know how to configure Apache, if necessary.
I know there are zillions of ways to do that.  I'd like some hints on how to tackle my problem, ideally using Bash or Python.  By the way, I've used Octave on CGI for some of this in the past, and I think it's excellent for math purposes, but I'd like to get ideas about some simpler, more generic avenues.
I would create a Django site for this. It can be setup really quickly. I would recommend you host it on PythonAnywhere. They have a free tier, and works really well. Django is similar to Flask, but I personally like Django. If you could be more specific on what your App needs to do, some sample code could be provided.
Create a web page which asks for some input and writes it to a file