Since Magento itself is too vast not only because of its features but also because of heavy number of files within it, it is really difficult to find which file is being used for what purpose and where that file is really located.
Magento has provided a feature in its configuration section in admin that allows us to enable template path hints. If we enable it, it will shows the file pathand block names.
To enable it:
1. Login to admin.
2. Go to System->Configuration.
3. Select a website from and click Developer tab in left.
4. In the Debug section, select Yes for Template Path Hints & Add Block Names to Hints.
5. Save configuration and refresh the front end page you will have some red blocks to indicate what files files are used in which block along with Block (class names) used.