I presume you are referring to WOrd, rather than Windows. In Word, there is a Tools drop down menu option with mail merge, which provides you with all the features you're likely to need. Although the system allows you to do this as part of the main job, I prefer to first set up the data file as a separate task. For this, you can typically use Excel. Name all the columns with meaningful titles that your mail merge can pick up and then, when you run MailMerge, you can point your word document at that document and off you go. The system is best used to create a new file (rather than over-writing the existing file). This will enable you to check yor output and back track if things go wrong.