I just installed a new template from http://themeforest.net/. My front end does not show all the components (banner, carousel, footer, etc.).
Can someone guide me how to customize my theme?
This is most likely due to the fact that your previous template was using different module positions to the new template you are now using.
All you need to do is simply open each of the modules that are not displaying as they should and assign them to a position that belongs to your new template.
For example, the default Joomla 3.x template (Protostar) uses position-7 for the right hand side, however another template may use sidebar-a.
To find out the module positions for your template have a look at the Demo and on the main menu, go to Features >> Module Positions:
Hope this helps
When installing a template into an existing Joomla install, it will never look like the demo of the new template. This is because all you've installed is the template itself and none of the demo materials. Unlike some other CMS's, most templates do NOT have things like carousel's built into them.
You have several choices: