Before building an showcase APP, you should first create a private key saved in the keystore file (Android showcase app maker provides keystore to save the digital certificate to self sign when the app run in Android).
1 Check the checkbox "Create new keystore", and click button "Next" (If you have created one, should skip to step 3) .
2 Browse a saving path for the key and name it (should not the existed). The forms whose tail noted by red asterisk is required and the others at least you have to enter one. Need to emphasize that the required form "Validity (Years)" is at least 25 years. And then click "Next" to create keystore.
3 If you have created a private key, browse the key from its saving directory and then enter its password. Click "Next".
4 Give your package file (need to continue to edit) a prefix provides convenience for remembering.As you see , you can enter the app version code and name (Once upload the same showcase app into the same Market, you should add the version code number one more).
5 Click "Next" to skip to the "Finish" window.
Note: The above 3 blue links: (1) open the output Apk file folder; (2) Go to FAQ: "How to publish android application"; (3) Go to FAQ: "How to test android application on a real device or emulator".