You can set the password with the GUI but it does not prompt you to do so when creating a new user. After you create the new user click on the password box marked in the following screen shot. As you have not set a password it will actually say Account Disabled for you. (Select the new user acct. on the left first)
You will be presented with the following, just enter the new password in the new password box and the repeat it in the confirm box. The current password for a new account is blank so you don't enter anything in that box. The final step is to click the Change box. You can now log in to the new account using the new password.
The procedure is the same to change a password that is already set you just enter the current password in the correct box.