Your admin password is the same one that you would use when you install most any software. It's also your account login password, which you would type in to log back in, after you would log out.
If you have totally forgot your account password, you can easily change it by restarting to your Recovery system.
Restart, holding Command+R
Choose Terminal from the menu.
enter the command resetpassword (no spaces, all one word), and press enter. The Reset Password utility will open. Enter a new password, then click Save, then Quit, and then choose Shutdown or Restart from the menu. Your Mac will show a login window this time, where you can enter your new password. That's what you would use from now on.