A family of Microsoft word processing software products for creating web, email, and print documents.
If a "fill-in-the-blanks" line has been created using underscore characters, the only way you can even sort of type on the line is to enable Overtype mode (usually you can do this by pressing the Insert key, but this function is disabled by default in Word 2010, so you'll have to click Insert on the status bar to change it to Overtype). Then press Ctrl+U to turn on Underline formatting. The underlined text in most fonts won't exactly match the underline characters, however.
For other ways to create lines you can type on, see http://word.mvps.org/FAQs/TblsFldsFms/LinesInForms.htm.
The exclamation point indicates that the document (or template) is macro-enabled; it will have the file extension .docm (document) or .dotm (template). So your hunch about macros may be correct, but if the sender of the document has not provided any instructions on how to use the form, you're on your own. There are better ways to create fillable forms, using form fields or content controls.