Preferably, use your e-mail provider's website. Go online with your favorite browser (I'm guessing Internet Explorer), go to your e-mail provider's site (www.gmail.com, www.yahoo.com or something like that), log in, compose new e-mail.
If you really want to write it using microsoft Word, all you have to do is write the message normally. When it's done, select everything (you can do that by holding down ctrl and pressing the "A" key), then clicking with the right mouse button, then selecting "copy". Starting composing a new message on your e-mail provider's, click the right mouse button, select "paste". Send the message.