> how does that "map" to "classic" inheritance, from Java or C++

I'd recommend doing it in two steps.

First, you need to get from the Java/C++ perspective of "classes are compile-time templates" to a perspective of "everything is an object". Python is a good example of the latter, as is Smalltalk (the latter is more 'extreme', but also less widely used):

    $ python3
    Python 3.8.9 (default, May 27 2021, 03:09:34) 
    [Clang 7.1.0 (tags/RELEASE_710/final)] on darwin
    Type "help", "copyright", "credits" or "license" for more information.
    >>> class A:
    ...   pass
    ... 
    >>> myA = A()
    >>> myA
    <__main__.A object at 0x10670c490>
    >>> A
    <class '__main__.A'>
    >>> myA.__class__
    <class '__main__.A'>
    >>> class B(A):
    ...   x = 123
    ... 
    >>> myA.__class__ = B
    >>> myA.x
    123
    >>>

Once you're comfortable with that, you can take the second step: from a Python/Smalltalk perspective of "everything is an object; when a slot isn't found in the instance, we fall back to looking in its class", to reach the Javascript/Self perspective of "everything is an object; when a slot isn't found in an object, it can tell us to look in another object". That 'other object' is the prototype.

All we're doing in the second step is removing a distinction: Python/Smalltalk have a built-in notion of "class", where some objects are classes and others aren't. Javascript/Self just have objects: we can use any object as a prototype for any other.