There is a huge literature on interpreting probability and this is even larger if you just look at examples of how people use it. A really good place to start is to follow the references mentioned in Hájek's encyclopedia article. A heavily overlapping list including lots of book chapters (among other things) can be found on Branden Fitelson's Probability and Induction course website: Syllabus

On the principle of indifference:

- van Fraassen, Indifference: The Symmetries of Probability
- van Fraassen - notes and references from Laws and Symmetry
- Laplace, A Philosophical Essay on Probabilities
- Hacking, Equipossible Theories of Probability
- White, Evidential Symmetry
- Novack, A Defense of the Principle of Indifference
- Norton, Ignorance and Indifference
- Mikkelson, Dissolving the Wine/Water Paradox
- Marinoff, A Resolution of Bertrand's Paradox
- Shakel, Bertrand's Paradox and the Principle of Indifference
- Williamson, Motivating Objective Bayesianism
- Seidenfeld, Why I am not an Objective Bayesian

- von Mises, Probability, Statistics, and Truth
- von Mises, On the Foundations of Probability and Statistics
- Jeffrey, Mises Redux (in Probability and the Art of Judgment)
- van Fraassen, Relative Frequencies
- Hájek, "Mises Redux” — Redux: Fifteen Arguments Against Finite Frequentism
- Hájek, Fifteen Arguments against Hypothetical Frequentism
- Hájek, The Reference Class Problem is Your Problem Too

Propensity accounts: