Showing the search results
By default the search results are shown with no distinction between those from local TYPO3 pages, records indexed, the file path and external URLs. Only division follows that of the page on which the result is found:

Basic view of search results
However, you can configure to have a division of the search results into categories following the indexing configurations:

Categorized view of search results
To obtain this categorization you must set TypoScript configuration in the Setup field like this:
plugin.tx_indexedsearch.search.defaultFreeIndexUidList = 0,6,7,8
plugin.tx_indexedsearch.blind.freeIndexUid = 0
The "defaultFreeIndexUidList" is uid numbers of indexing configurations to show in the categorization! The order determines which are shown in top. Changing it could bring results from typo3.org in top:

Categorized view of search results with a set order for categories
The categorization happens when the "Category" selector in the "Advanced" search form is set like this:

Choosing categorization in the advanced search form
(Notice, you can preset this value from TypoScript as well!)
Searching a specific category from URL
If you want search forms on the site to make look up directly in results belonging to one or more indexing configurations you can use a set or GET variables like these, here using UID values 7 and 8 since they look up in typo3.org results:
index.php?id=78&tx_indexedsearch[sword]=level&tx_indexedsearch[_freeIndexUid]=7,8