Hi Mahendra,
1). is it a admin tool or there is anything for developer too ?
It is very much a developer tool as well, it involves implementation and a set of API developer tools are also available.
2). how to download this tool ?
This tool is a cloud based tool. Also, it is an enterprise tool which means your firm would have to purchase a product license only then you can use it
3). best sources to learn it.
Since you don't have license the best sources would be the adobe analytics documentation - https://marketing.adobe.com/resources/help/en_US/reference/
You can also look for the Adobe Analytics youtube channel - https://www.youtube.com/channel/UC8I6bqCk7gO6YdoMz6W5fvw
Also, there are a lot of blogs one of which is this one by Adam Greco - http://analyticsdemystified.com/blog/
I hope this helps.
Tanmay