By following this guide, you will learn how easy it is to export any installed app on your Android device. Why is this useful, you ask? Well, I can think of two good reasons right now. For example, if you would need to decompile an apk, you would need to export it first. After that, you can do anything you want with it. The other one is even more interesting. When you buy a app, you have 15 minutes, to try out the app and then refund it. Many things can happen in these 15 minutes :).
First off, you will root access to your phone. If you do not have it and want to take care of that yourself, I recommend guys at XDA developers. They know their stuff and you will most definitively find a good tutorial on rooting your phone over their forums. The second one, you need to install the Root Explorer application. The free version is not good enough for this tutorial. After this its smooth sailing from now on.
Download your desired application from Google Play and wait for it to be installed. Afterwards start up the Root Explorer. You will be prompted for root access, which you must grant. Tap the data folder, then app and you will get a list of all installed applications. Long press on the recently installed application and choose copy. Go two folders up, scroll down to sdcard and tap on paste. This will copy the apk file on your sd card. If you do not have one, then copy it somewhere else it does not matter where exactly. That is all there is to it, exporting an android application is really simple.