Running a .java code from another .java code

i have two java programs, one is the main program and other one is a selenium script. i have to run the selenium script from the main java program. I have tried using reflection but didn't get the exact understanding of how reflection works. I would be so helpful if someone can provide me some insights of how reflection works and how i can use it(small code snippet if possible).

And if anyone have any other recommendation for this use case you are welcome.