Like with any custom Joomla template you should define all of your newly created module positions in the template.xml file. This is the Joomla template file that holds a lot of the information about the template including the name, author and of course, all of the available module positions in the template. You don't have to add in all of the positions but it is seen as good practise to so when a user is selecting a module position from the module manager in Joomla, it will automatically appear in the list without the user needing to guess or manually type in the name of the position they want to use.