The required password is your Operating System Administrator password. It has nothing to do with Adobe or your account here.
Man,i install the abdobe flash player,it sayed install completed,but after i dont see the app in my pc!WTF?
What OS are you using? What browser are you using?
Adobe Flash Player is not a desktop application. It is a plugin.
If you are using windows, you can see an entry of Flash Player in your control panel depending on which Flash Player you have installed. Similarly, if you are using Mac you can see an icon of Flash Player in system preferences.
You can also check if Flash Player got installed successfully by browsing to Adobe - Flash Player page in your browser.