This APK file will work in any compatible android phone but it contains an internal debugging key which is not acceptable if you want to publish in Google Play. Google Play need your APK file to be signed by yourself before publishing. It is very easy to create a key and sign the APK.
Just you have to left click on the project folder "sample" and select "export" (see image below)
Now select Export Android Application and click NEXT (see image)
On the next screen you can see the project name "sample" just click next (see image)
Now click on create a "new key store" as you are making a key for the first time. (see image below)
Next time onwards you can use the same key to sign all of your projects.
Now you have to save the key to a file, so click browse and type a file name and click save.
You have to give a password for the key, you have to remember it, as it will be asked when next time an APK is signed. Type the password again to confirm.
Now you click NEXT
On the next screen you have to give the details for the key. Give the following details. (see image below)
Alias name: you can give your name
Password: just the same password you typed before
Validity: Give a big number like 100 Years.
Organisational Unit: Give any name like your family name
Organisation: Give some name as above.
Country code: Search for it in Google.
When finished, Click next to continue
On the next screen click browse and save your signed APK file in to a folder or desktop. Click finish to complete the setup.(see the image below). Congrats!! You can now publish it in Google Play.
(TIP) Please remember that you have to give a one time developer fee of $25/- for publishing in Google play. If your package name start with com.example, com.google or com.android they will not accept your file. better you can give a starting name as "com.yourname" because it is to be unique in Google Play.
(TIP) If you didn't change your package name while creating the project, Eclipse create your package name as com.example, to know how to change the package name go to this CHAPTER
Also before publishing you have to make to screen shot of any of these types (see image for details)
320x480,480x800,480x854,1280x720,1280x800 , 24bit, PNG or JPEG
Also a high resolution Application icon of 512x512, 32bit image jpeg or png Max.1024KB
As optional you can upload promotional graphic image of 180x120,24bit PNG or JPEG
Optional feature graphic image of 1024x500,24 bit PNG or JPEG
if you save normal images it will be 24bit. If you want 32bit image you should save as web image in Photoshop or add alpha (choose layers > Transparency>add alpha channel>save as PNG )to it in Open sourse GNU Image Manipulation Program (GIMP, click to download)
You may also create optional youtube promotional videos. All these optional items will make your app more attractive.
If you want to publish it free of charge then go to SlideMe (TIP) They don't accept simple applications, for that visit Android Freeware (TIP) You have to upload the APK file in to a file sharing site like Rapid Share First.
Click the link below to visit
Google Play Publish Page