I found this on developer.android.com, is that mean that I can't use Eclipse to develope Android aps??
P.S. : I use Ubuntu 15.04 64 bits
"Important: Support for the Android Developer Tools (ADT) in Eclipse has ended, per our announcement. You should migrate your app development projects to Android Studio as soon as possible. For more information on transitioning to Android Studio, see Migrating from Eclipse ADT. "
Well, I don't like to cite someone, but this explanation of above problem is pretty enough good:
You still may be more productive with Eclipse at the time of writing, as Android studio is relatively new and some obvious features (like Unit testing, for instance) are kind of present yet you just cannot get them working. It will pass many years till Android 6.0 applications you can develop with Eclipse no problem will no longer run on majority of devices on the market.
But as Android studio will likely to improve over time, and new features will be available only there in the future, I would recommend to start from that IDE for a complete beginner. Even better it may be to understand how the command line development works as this may allow to use any flexible enough IDE, does not matter is it officially supported on not.
For beginners who just started Android Development, it's good to start with Eclipse because of many tutorials and books are based on using Eclipse with ADT plugin.
But look... there you would not find big projects with some libraries and dependencies or modules, but TicTacToe, simple GPS Provider who would tell you where you actually are or ImageGallery.
Notice also how many StackOverflow question tagged with android and eclipse tags are because of incompatibility of dependency, module or library. Take your time and have a look into it.
Times are changing... Two years ago there wasn't Android Studio and today's must-have libraries like Picasso or Robolectric.
Hope it help you to understand above statement.