Define "quick". The usual way would be the Android SDK, possibly in combination with the Android support of an IDE like Eclipse or IntelliJ. Or check out App Inventor and see how far it gets you. There are no short cuts, though - if you've never done Android development, you've a learning curve ahead of you.
Tools as in say the Eclipse IDE where you can develope apps,
There are lots of apps that can be made in java.
there are some steps to integrate andoid SDK in eclipse for that you can search.
Number of links available on internet.
Before you start creating Android application, be sure you have your development environment set up. You need to:
1. Download the Android SDK.
2. Install the ADT plugin for Eclipse (if you’ll use the Eclipse IDE).
3. Download the latest SDK tools and platforms using the SDK Manager.
Are you looking for android development or a tool that can somehow generate an android app for you ?
You said its for your site. Does that mean you want your website to easily render on an android device ? or does it mean you need a dynamic facility in your site that you want to replicate in android (such as fixing an appointment and similar)