Start with the tests, examples and apis; at least implement a couple of parts of the api, whether a plugin, or using the code as a library depending on what the

Start with the tests, examples and apis; at least implement a couple of parts of the api, whether a plugin, or using the code as a library depending on what the code does. Once you understand those, read the headers of the apis you can follow the code through to the rest of the application. Usually, a project will use 3rd party deps so you will have to understand at least the apis of those as well. If the project uses cmake or whatever build system builder, learn it inside out. If its just a Makefile then thats simple enough to understand, follow how everything is compiled and linked together.