All current genealogical programs (Click here for a list of popular programs.) use their own proprietary file format for storing and manipulating genealogical data. This makes it very difficult to share this data with other family tree researchers using genealogy software from different publishers. To solve this problem, a standardized file format has been developed so this data can be easily shared electronically regardless of the software used. This standardized file format is called GEDCOM.
A GEDCOM file is a file type that has been developed for GEnealogy Data COMmunication between different genealogy programs. Basically, a GEDCOM file is a text file formatted in a way that is readable (and understandable) by all genealogy programs currently on the market. (Click here for a list of popular programs.) The GEDCOM file format is used to share genealogical information between users of these genealogy programs. Most genealogy programs will export a GEDCOM of all or part of the loaded database and can import one of these GEDCOM files, either into an existing database, or into a new empty one.
Here's how I recommend you use a GEDCOM file (I've used my own RootsMagic software as an example; the process is the same for other current genealogical programs.):
Download the desired GEDCOM file from the Internet or other source onto your computer.
Close any genealogy data files you are currently working on (keeping your genealogy software running).
Create a new (temporary) genealogy (ie RootsMagic) data file with a name different from any you've worked on in the past.
Find the software (RootsMagic) command for importing GEDCOM files (probably in the "file" menu).
Import the GEDCOM file you downloaded.
You have now created a RootsMagic file containing ALL the data in the imported GEDCOM.
You can then use your software to easily review, edit, delete, or add to the data you've downloaded.
Depending on the contents and size of the GEDCOM file you've imported, you will likely find lots of information you don't want or need. For example if the GEDCOM you downloaded was from my Zadock Judd website you'd probably find some data on my family tree that pertains to your family tree and some that doesn't. You likely don't want the unrelated genealogical lines filling up your hard drive.
In your genealogical software, select the names and data you want to keep and export this selected data to a new GEDCOM file with a new name.
Close and/or delete the temporary RootsMagic file you created in step 4.
Reopen your regular RootsMagic file (probably the one you closed in step 3).
Go to the "file" menu and import the GEDCOM file you created in step 10.
Your data will now likely have duplicate entries for some (or many) of your ancestors. Use the features of your genealogy software to merge the new data with the data you already have. This will eliminate the duplicate entries.