If you want to set up Netbeans to allow you to develop Android applications there are three places I suggest you visit.
The first is where you can pick up the official SDK for your OS. It will also walk you through setting up Eclipse, but that isn't the IDE I use and I didn't want to install it just for Android projects.
The second place I think you should go is to an old blog post discussing getting Netbeans Setup to play with Android, whilst it was written in 2009 the links from it are accurate and the information sound.
Finally if you get stuck setting up the SDK I would suggest watching the following YouTube video; It is assuming a Windows based OS but the guide is easily transferable to other operating systems.