i am installing Adobe Flash Player now, at the end they ask me the password, but I don't know what password they need, what should I do?

I'm assuming that you're on a Mac.  If not, please give me some details about your system: Read Before Posting: How To Get A Useful Answer To Your Question

This password prompt is presented by your operating system, and is intended to keep you from accidentally installing software.

If this is your personal machine and you don't need a password to log into the computer when it first starts up, you can probably leave the password blank and click OK to get past this prompt.  If this is your personal machine and your normal password isn't working, check to make sure that CAPS LOCK is off, and type the password carefully.

If this is your work machine and it's asking for an Administrator password, well, you'll need to have a conversation with your friendly IT person.

If you're still stumped, you may need to reset the password on your Mac:

http://support.apple.com/kb/PH18653

http://support.apple.com/kb/PH14325

http://support.apple.com/en-us/HT201240