I want to know this because I want to do something “amazing” with the mouse, with zoom in and out, etc.
Google maps are provided to the user as HTML + CSS + JavaScript (except Street View, which uses Adobe Flash). If you want to use the excellent JS libraries, check out the link to the Google Maps Javascript Reference - this is completely understandable and includes many examples.
Also check out these excellent tutorials - although they were written for the GMaps API version 2, they can easily be modified for the current (version 3) API.