I am trying to figure out a way to expose the functionalities of SalesForce via API so that I can use my business logic with my custom Android app/web-page which calls API via POST.

However, I have been unable to find a comprehensive solution. Any help will be greatly appreciated as I am aware of functionalities of SalesForce. But, I am not aware of exposing the Apex class as an endpoint.

This is what I would like to do as a basic starter:

Write an Apex class which takes two numbers as inputs and returns the sum of two numbers. I do know to do this via Lightning Component and I have read about VisualForce page. However, I have a requirement where I have to integrate SalesForce with vanilla HTML, Javascript and CSS if possible. So, POST would be convenient.

My attempts before asking this question:

I read lots of official documentation. I also got to know about Session ID and how that is being protected in developer console and how I can get it via workarounds. All nice. But, these official documentations did not help me design one Apex class which can do the use case mentioned above. I read lot of community posts which were more helpful. But, I have been unable to cobble them up together and test it via postman. Thanks for the time and consideration.

I am trying to figure out a way to expose the functionalities of SalesForce via API so that I can use my business logic with my custom Android app/web-page which calls API via POST.

However, I have been unable to find a comprehensive solution. Any help will be greatly appreciated as I am aware of functionalities of SalesForce. But, I am not aware of exposing the Apex class as an endpoint.

This is what I would like to do as a basic starter:

Write an Apex class which takes two numbers as inputs and returns the sum of two numbers. I do know to do this via Lightning Component and I have read about VisualForce page. However, I have a requirement where I have to integrate SalesForce with vanilla HTML, Javascript and CSS if possible. So, POST would be convenient.

My attempts before asking this question:

I read lots of official documentation. I also got to know about Session ID and how that is being protected in developer console and how I can get it via workarounds. All nice. But, these official documentations did not help me design one Apex class which can do the use case mentioned above. I read lot of community posts which were more helpful. But, I have been unable to cobble them up together and test it via postman. Thanks for the time and consideration.