So this whole "is the external world really there?" question is pretty tiresome: it's the bane of intro philosophy students and the thing that turns off many of these students from ever taking another philosophy class, yet it's still pretty much the central concern of epistemology for much of its history.
Edmund Husserl asks if we can't just set that question aside and describe the phenomena of our experience. Without labeling the experienced world as truly external or truly our invention, either of which involves theorizing beyond what's actually given in our experience, let's just see if we can give a theory-free description of things and see what that reveals.
Well, for Husserl, escaping from theory-laden ordinary language in describing phenomena requires inventing a lot of cumbersome terms that make him hard to read, but for this reading, Cartesian Meditations (where, just as it sounds like, he uses a parallel structure to Descartes's method of doubt as depicted in the Meditations), we've got a transcription and elaboration of some lectures Husserl gave in 1929 (lectures typically being not as obnoxiously opaque as philosophers' writing), so it's not as thorny as most of his other writings, and it serves as "An introduction to phenomenology" (that's the subtitle of the work), which is a movement we've talked about several times on the 'cast that includes folks like Heidegger, Sartre, Merleau-Ponty, plus many other philosophers analytic and continental make use of the basic method of trying to describe experience without imposing theories upon it. In this respect, it's just a thorough-going empiricism, which unlike classical empiricism (Locke, Hume) doesn't include elements like "sense data" that in fact aren't experienced.
Read the text online. I'm sure we won't actually get through the whole text, but don't know specifically where we'll stop. The introduction and first couple meditations should have most of what we need.