The first part of this process is obviously is the downloading and installing the android Software development kit (SDK) . You can find it on the official website for the android developers here.
This site provides with each and every detail regarding the download and install of the SDK so you need not worry about it.
Now talking about something called as Android SDK Tools, which are a part of our android SDK. These are tools needed for the development of android applications.They get saved inside the android sdk's tools directory.
Revision of android SDK tools: the SDK tools are revised and are made available to the developers by the android developers community. So If you are downloading the SDK for the first time then you can directly download the latest version but If in case you already have the SDK downloaded you can update the SDK tools to the latest version/revision available.
As of now the latest revision is Revision 20.