Generate all possible test papers from txt files

I would like to build a simple program in Java. But I don't know where to begin. What should I think of when developing a flow or pseudocode before programming the solution.

I have two txt files, containing questions. One file has 60 questions and the other 432 questions. I would like to generate a test paper and export it to an txt file, for example 10 questions out of 60 and 12 questions out of 432

However, I would like to calculate how many variations are possible? And subsequently I would like to generate them.

Could you guide me in thinking, and how to devise something,

I don't want a complete solution, because I would like to challenge myself to develop/program it. But a start and what kind of classes/methods are needed?