When you choose a position for your module in the Module manager of your Joomla application, the drop-down menu will only display a list of positions that have modules enabled in them. If you have not installed the sample data for Joomla, this list may contain only one available position for your module.

The solution is simple, you can type the position name in the "Position" field. If this position is enabled in your template, the module will be displayed in the selected place.