How to do something on the site using the code?

Question

Programming languages

Hello everybody!
For some time I have been automating repetitive actions on the Internet using a program similar to Autohotkey.
I was no longer satisfied with the speed of execution, because the screen image is analyzed there and button presses and cursor movements are emitted.
As far as I understand, it is possible to analyze the page code and, depending on what will be there, perform one or another action. And text analysis is much faster than image analysis.
But I absolutely do not understand how this is done, in what programming language to write such a thing, and how to run the code in general.
For example, I have a task: there is a link to some VKontakte post, if such a post exists, then you need to like it.
Please tell me on what / how to write code to do this.