You assign a module to a position using the module manager.
On the left side of the page, on the third line, there is a drop down menu that lets you select the position. Modules that are not published will not display.
Modules can be assigned to unused positions (positions not in the template) if you want to have them published but not displayed in a position (for example, if you want to display a module in content).
Multiple modules may be assigned to the same position. They will be displayed in the order shown for modules in that position in the module manager.
If you want to display a module in more than one position, use the module manager to copy the module and assign the copy to the second position.
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