No build target while creating new project

I am a .NET developer and I wanted to work on mobile development though Java. For this I have download eclipse, SDK, Android SDK, ADT plugin and Phone Gap as m开发者_如何学Goentioned in this URL.

http://www.phonegap.com/start/#android

For me everything went successful. But when I am trying to create new project I am getting below Screen:

My Questions:

1. Why I am not getting any build target? Am I missing something?
2. What is Package Name ?
3. What is create Activity?

I apologize if you find my questions very small or useless but as a beginner these are very important for me

Edit1

Android SDK Installation

Edit2

When doing Window > Android SDk and AVD Manager

You need to install the Android SDK and install an Android platform package. See this guide to installing the SDK: http://developer.android.com/sdk/installing.html

If you have already installed the SDK then you need to follow step 4 from that guide to install a platform.

1. From within Eclipse, select Window > Android SDK and AVD Manager.
2. Choose a platform - ie 2.2, 2.3 etc:

Re: Edit #2 above, go to Eclipse Window->Preferences and configure your Android SDK to point to your SDK folder, looks like d:\program files\android\android-sdk\ from your screenshot

Package name is your starting folder structure to create.

Create Activity creates an initial activity class for you within your package