In the Android SDK Manager, if you expand any API, you see packages saying things like ‘SDK Platform, Google APIs’ and also many other packages like ‘Real3D, Bionic’ etc. Screenshot:

My question is, what’s the difference between all these packages, and which packages do I need to install if I want to create virtual devices for some of the most common android configurations? Do I need to install SDK platforms, Google APIs, or any of the other packages in order to create emulations?
And what’s the difference between SDK platform and google APIs?
You need following
1)SDK Platform (2.2,2.3 or 4.0.. depending on your need)
2)SDK Tools/SDK Platform tools ( to build, test and debug apps)
Google API’s acts as an interface to Google Map , While SDK Platform will provide access to platform(2.2, 2.3 etc) specific API’s.