If you want to update your Facebook account with your Twitter updates, install Twitter's Facebook app in your Facebook account
You can add Twitter's Facebook app while you're logged in to Facebook. You can search for Twitter in the Facebook application directory, but why not just go straight there. Once you're on the app page, click Go to Application. (Note: you may need to log in to Facebook to access some of the FB links in this help article.)
After you've done this, you'll have to allow Twitter to access your Facebook account.
Next, enter your Twitter user name and password into the log in boxes.
Ta da! Now you can update your Twitter account from Facebook. If you want to allow your Twitter account to update your Facebook status, click the link displayed at top; this means everytime you post a tweet, it updates your Facebook status as well.
Facebook will ask you to approve the request, and then you're done!
To add the Facebook application from Twitter, visit our widgets page and select the Facebook tab. Click 'Install Facebook in Twitter' and we'll take you over to Facebook to walk you through the above process. You're on your way!
If you search Facebook's application directory for Twitter, you'll see a few other apps that allow you to do more with Facebook and Twitter.
The Twitter Updater allows you to do the opposite of the Twitter app, and sends a tweet to your Twitter friends whenever you update your Facebook status. For those of you who use Facebook more, but have friends who use Twitter, this is a good way to keep your Twitter friends posted!
If you want to get fancy, you can use the Selective Twitter Status app to control which of your tweets appear in your Facebook status.