Online newspapers are those that can be accessed on the web and read with web devices like desktop computers, laptops, tablets and smart phones. Most newspapers that have been published recently or published in the past few years can be read online with these Internet devices.
Historical newspapers are older newspaper editions and many of these newspaper editions have been microfilmed and can only be read with microfilm readers. Most libraries and historical societies have microfilmed copies of older local newspaper editions and microfilm readers for reading these newspapers.
Currently there are a number of groups that are digitizing microfilmed newspaper editions and so now many of the older editions can now be read online using a desktop, laptop, tablet or smart phone.
An index refers to a list of names, places and topics along with the pages on which they can be found - similar to the indexes found in the back of most books. Most online newspapers have been indexed so that articles can be found based on keyword searches. So for example, someone might enter the surname "Brown" into the search box for an Historical Newspaper and the search results will indicate the newspaper editions where the name Brown can be found.
There are two major ways to index Historical Newspapers - manually and using computer algorithms.
Newspapers that are online in machine-readable text format are usually indexed with computer algorithms that read each newspaper edition and determine which words or terms should be indexed. These indexed terms are then referenced to the publication dates and page numbers of each newspaper edition where the indexed word or term appears.
Historical Newspapers that have been digitized (primarily from microfilm copies) can be indexed using computer algorithms but they are not always accurate and so many of these historical newspapers have been indexed manually. In some cases parts of these historical newspapers have been indexed manually. For example Family Search Indexing has and continues to index obituaries that were contained in many historical Newspapers.
Most Online Historical Newspaper sites provide search capability for their indexed editions and so visitors can search all editions of one or more newspapers with a single click.
Most of these sites have "advanced search" features so that visitors can search by date ranges, fields and phrases. Many sites also provide the option for a refined search or additional search based on the results of the initial search.
You can use search engines like Google, Bing and Yahoo to find a particular newspaper or a multiple newspapers published within a geographical area.
Local and state libraries are also good sources of Historical Newspapers. There are also national lists like Historical Newspapers Online provided by the University of Pennsylvania.
Think of an historical event that affected members of your family - like World War I, World War II or other military conflicts. Or perhaps the 1918 flu pandemic (the Spanish Flu) that killed over 50 million people worldwide.
More and more historical newspapers are now indexed by keywords. So just enter the historical event that interests you and search the historical newspaper database.