App Development

Hello, I want to make a simple mobile app that would take input from the front proximity sensor of the phone and count how many times something came in front of it.

Kindly tell me the foundational skills and language I would have to learn to get started?

Knowing basic programming concepts (data types, function, conditionals, loops, control flow, classes, methods and more) is a must

Language depends, if you want to build native apps: for IOS the latest swift version. for android a language that supports JVM (Java and kotlin are the two most popular so far I know)

you could also build a hybrid app. I found a good article:

https://medium.com/@OPTASY.com/what-hybrid-app-development-framework-should-you-use-for-your-projects-in-2020-top-3-999662b30cce

The question in your case (something you will need to research) is if the hybrid framework of your choice is capable of reading the sensor.