Google has provided one single download which contains everything that you need to install ADT Bundle on your computer. This single compressed file download includes Eclipse with ADT plugin, Android SDK tools, Android platform tools, latest Android platform and system image for the emulator.
After your download is completed, depending upon your system, you will come across a download file like adt-bundle-windows-x86-20131030.zip. Extract this file to a location on your hard drive. You will have almost everything that you need as an Android developer. The only thing missing from this download is Java Development Kit or JDK and Java Runtime Environment or JRE.
JDK and JRE can simply be downloaded as one single bundle from the oracle website. They have bundled it as Java Platform, Standard Edition or Java SE. This single download contains JDK (Java Development Kit), Server JRE (Server Java Run Time Environment) and JRE (Java Runtime Environment). This is one heavily updated package with new versions coming out all the time.
You will find the download button at the page above. It is listed as Java Platfrom (JDK) 7u51. The u51 part might change, depending upon their current release version number. Once you click on download, you will be redirected to a page where you would have to accept “Oracle Binary Code License Agreement for Java SE”. Once you accept to this license, you can download Java Platform file from the list. Your download file will be named something like jdk-7u51-windows-i586.exe depending upon your OS. Download it and install it.
Now, you are done with downloading everything that you need to be an Android developer. The next thing to do to begin developing is to run Eclipse. This is the Integrated Development Environment or simply (IDE) for Android.