YOnce the basic setup is done, yo need to tweak your Joomla installation to behave as you need. you will need individual configuration settings for your website elements (components, plugins, modules, content pages, templates): in the Joomla lingo we call them options. These options are applied to the whole website, for users, categories, modules, components. Since Joomla 1.6 this has became standard: you will always find an icon named Options in the backend pages, which are providing you the interface to set your preferences for the given component.
For example in the Joomla 1.6+ in the template manager you have in the Options a way to switch on or off the support for the well known trick to append "?tp=1", which reveals you the available module positions for your templates.
Now you can block attempts to visualize by others these module positions by visiting the address:
BTW: The "tp" stands for template position and the trick is one of core Joomla tricks.