There's sometimes danger in opening attachments - they can cause harm - only ever open attachments from trusted sources.
A file attached to an e-mail will have been created from some application at the sending end - a Word document (.wd) - an Excel Spreadsheet (.xls) Portable Document Format (.pdf) Rich Text Format (.rtf) etc etc - there are Thousands of file types.
The letters following the dot are called the Extension and are the key to the type of file and aslo to the application YOU need to open it.
If there are any files you're unable to open make a note of the Extension and use Google to discover what application can manage files with that extension.
Save the files and open them using the appropriate application.
Peccavi
October 2009