To add a user simply click the user manager icon on your task bar.

Click User >New User from the menu.  Enter a username and the password twice as shown. Click the boxes as shown then click the Add button.

Here's a trick in case you need to give a user Administrator privileges so they can log into the desktop. WARNING ! WARNING ! Do NOT give admin access to just anyone. Only to those you would trust without question.

Open the user manager as above. Double click the user you want to give admin access to. The screen below is shown.

Click the groups button and add the user to the administrators group as shown below. Select Administrators and click the add button. This makes the user a member of the administrator group. You can remove the user from the admin group at any time which will disable all admin features including desktop access. Only those in the admin group can access the desktop.