Users and Groups is for your admin password - the same one that you would use for login to your Mac, and also the same one that you use for installing software. The admin password is NOT in any way related to your wifi security password.
If you have forgotten your normal admin password, then you can reset that password, either by using the terminal, resetpassword command when you boot to your recovery partition, or you can also reset your new user setup, then reboot so your Mac takes you through making a new account and password.
Or, alternatively, you can enable the root user, and simply change your admin password in your normal account while logged in to your root account.