How to Send a Message on Facebook
You can generate Facebook’s basic New Message Window by clicking the Messages shortcut in the big blue bar on top (it looks like two overlapping word bubbles) and clicking the Send a New Message link from the menu. The New Message window then opens.
This dialog box has only two fields for you to fill out: a To field and a message box where you type the text of your message. If you’re used to using e-mail, this may strike you as a little odd because it doesn’t have a Cc, Bcc, or subject line.
One trait of e-mail is how much it mirrors the formal letters people used to write, whereas now, most people spend a lot of time writing quick notes to the people they see the most. Except for work messages, most of our e-mails are sent to our spouses and our friends. Given that Facebook is all about friends, you're not very likely to require that subject line.
To address your message, simply start typing the name of the friend you're messaging into the To field. Facebook autocompletes with the names of your friends as you type. When you see the name you want, highlight it and click or press Enter. You can type more than one name if you want to have a conversation with more than one person at the same time.
You can send a message to people’s e-mail addresses if they aren’t yet on Facebook (although if they aren’t yet, it’s truly their loss). Simply type the full e-mail address into the To field. Separate multiple e-mail addresses with commas.
Type your message into the message box. Messages can be long or short, silly or serious — whatever you have to say. If you want to add a link to a website or article to a message, you can copy and paste it into the message box. Facebook then generates a preview of the article so your friend has more info before clicking the link.
This is very similar to the way the Share box works when you add a link to a post or status update, except instead of sharing the link with all your friends, you're sharing it with just the people you're messaging.
Two icons beneath the message box represent features that are entirely optional and infrequently used, but just in case, here’s what they are:
Add Files: Much as it does in many e-mail programs, the paperclip icon signifies attaching files to a message. Clicking the icon opens an interface for searching and selecting files from your computer’s hard drive. You can attach photos, videos, documents, and so on.
Add Photos: Though you can attach photos by clicking the Add Files button, if you want Facebook to generate a preview of them for your intended recipients (as opposed to having to download and then open them) use the Add Photos button. This will again open an interface for searching and selecting photos from your computer’s hard drive.
When you’re done writing your message, just click Send and be on your way. Your friends will receive the e-mail in their Facebook Messages Inbox, and Facebook notifies them with a little red flag on their Home page. Depending on their account settings, they may also receive an e-mail in their e-mail Inbox letting them know about a message in their Facebook Inbox (yes, it’s a little redundant).