I need to upload my own new second Android application in playstore. I know it is possible to use same keystore file. But I don't have idea to use same alias or different alias need to generate for second application for playstore.
Keystore is just container holding your keys (like jar for cookies), so from technical point of view is completely irrelevant if you keep all your keys in single keystore or you have them splited among many (you can even have separated keystore file for each key - nothing prevents that).
Alias is also irrelevant - it's just "human friendly name" for your key, just for your convenience. It also makes no difference technically, however you cannot have more than one keys using the same alias in given keystore:
All keystore entries (key and trusted certificate entries) are accessed via unique aliases.
However you can use the same alias in different keystores w/o any problems.
NOTE: You can technically sign all your apps with the same key but this is strongly discouraged. You should create separate key for each released app - that will make your life much easier when i.e. you will decide to sell your project for instance.