I am complete beginner in this field. I am studying this paper 'Study of Anisotropic Compact Stars in Starobinsky Model'. Here in this paper, https://arxiv.org/pdf/1412.2120.pdf , I am confused about how the author wrote the matching conditions as shown below in the image. I have gone through the references written in the paper, but I can't find the form as given in this paper ? Anyone has idea or is there any reference of how is this derived ?

I also want some advice about researchwork. For example, I am not much proficient in f(R) gravity and theories, but I just know about procedures. I am actually working with a group and we make our metric and from previous studies we assume solutions of spherically symmetric metric and then try to match our model with available data. I want to know is this okay to proceed in this manner, or should I go through all the references given here.

I have also found this one: https://arxiv.org/pdf/0711.1150.pdf - "Junction Conditions in f(R) Theories of Gravity" Is this relevant one to here? If yes, how and if no, how ?

How much common is this for a "good" researcher that (s)he stuck with something or not able to understand, or you know, I am trapped in studying these references/prerequisites.

Also, this is my first question in this community website. If I have broken any norm then please inform me.