Working with theory is all about how you will apply a theory to structure your research. Whether you choose a model or theoretical framework from health theory or from the interdisciplinary work, you will have to understand the theory on its own before you can apply it to your research.
You can use many of the same resources to look at the literature on your theory that you use to look at your topic. The hard parts are:
Here are a few online books on theory to get you started.
But remember to use the literature search tools you learned in module 2, along with the reading you have already done, to look for other material! Finding a theory that you've seen discussed "in action" through interesting articles may be better than looking through books of theory.