The Google Maps API allow for the embedding of Google Maps onto web pages of outside developers, using a simple JavaScript interface or a Flash interface.

Google Maps API does two major things:
It can cause maps to appear for the user.
It can return data about a latitude/longitude location, or return data about an address.

For a while now, Google has made it a little harder for people to use custom Google Maps on their websites by requiring a API key for each website. So first you need to get yourself such a key. The API key is a unique identifier that is used to authenticate requests associated with your project for usage and billing purposes.

The Maps Static API service creates your map based on URL parameters sent through a standard HTTP request and returns the map as an image you can display on your web page. The API HTTP services can be accessed over a secure (HTTPS) connection by Google Maps API Premier customers.

The Roads API allows you to map GPS coordinates to the geometry of the road, and to determine the speed limit along those road segments. The API is available via a simple HTTPS interface, and exposes the following services:

Nearest roads This service returns individual road segments for a given set of GPS coordinates. This services takes up to 100 GPS points and returns the closest road segment for each point. The points passed do not need to be part of a continuous path.

Snap to roads This service returns the best-fit road geometry for a given set of GPS coordinates. This service takes up to 100 GPS points collected along a route, and returns a similar set of data with the points snapped to the most likely roads the vehicle was traveling along. Optionally, you can request that the points be interpolated, resulting in a path that smoothly follows the geometry of the road.

Speed limits This service returns the posted speed limit for a road segment. The Speed Limit service is available to any Google Maps Platform Premium Plan customer with an Asset Tracking license. For Google Maps Platform Premium Plan customers who transitioned to pay-as-you-go pricing, the feature remains active. Use Google Maps Downloader to download maps in image format on your PC.

Which APIs are enabled by each product?
Each product (Maps, Routes or Places) enables a set of APIs. You can select multiple products, and use as many of the APIs in each product as you'd like. Here are the APIs enabled within each product:

Maps: Maps SDK for Android; Maps SDK for iOS; Maps JavaScript API; Maps Static API; Street View API; Maps Embed API.
Routes: Maps JavaScript API, Directions API; Distance Matrix API; and Roads API.
Places: Places API, Places Library, Maps JavaScript API; Geocoding API; Geolocation API; Time Zone API; and Elevation API."