Go to Tools on the menu bar

Select Mail Merge

Choose "Create" -> Form Letter

Select "Active Window"
 
 

Now choose where you will get your data from:

Change the file type to look for a database

Open that database that you want to use in you mail merge form letter.

Choose the Table you created in your database.

Now you are ready to "Edit Main Document"

Start typing your letter in the document. When you are ready to insert a field select: "Insert Merge Field" from the tool bar.

If you want to "See" how your letter will look for each person you are mailing choose: <<ABC>> from the tool bar