Hi Kathryn,
The 49 processes are described one by one in the PMBOK Guide, but there are times when you bounce from one to another and back again in rapid succession. They are not always linear, either. They intersect and run in tandem in some cases, more like a circular process. That said, for me, I
roughly learned the first two Process Groups, Initiating and Planning, vertically on the PMBOK Guide's table, p. 25 of the 6th Edition. Then, I learned the last three Process Groups, Executing, Monitoring & Controlling, and Closing, in horizontal or circular steps.
You're wise to have a good understanding of the 49 processes. Starting in 2021, half of the PMP exam's questions are based on a predictive/waterfall approach, which is based on the PMBOK Guide. PrepCast has an article about them,
The Complete Guide.
Wish you the best, Kathryn!