Embedding Python is similar to extending it, but not quite. The difference is that when you extend Python, the main program of the application is still the Python interpreter, while if you embed Python, the main program may have nothing to do with Python -- instead, some parts of the application occasionally call the Python interpreter to run some Python code.
So if you are embedding Python, you are providing your own main program. One of the things this main program has to do is initialize the Python interpreter. At the very least, you have to call the function Py_Initialize() (on MacOS, call PyMac_Initialize() instead). There are optional calls to pass command line arguments to Python. Then later you can call the interpreter from any part of the application.
There are several different ways to call the interpreter: you can pass a string containing Python statements to PyRun_SimpleString(), or you can pass a stdio file pointer and a file name (for identification in error messages only) to PyRun_SimpleFile(). You can also call the lower-level operations described in the previous chapters to construct and use Python objects.
A simple demo of embedding Python can be found in the directory Demo/embed/ of the source distribution.