In some applications on your phone such as Camera and Photos, you will see two Facebook options in the selection menu when you share your photos:

If you already signed in to your Facebook account when you turned on and set up your phone for the first time, select Facebook for HTC Sense to upload one or more photos to that account. For details on Facebook for HTC Sense, see About Facebook for HTC Sense.

Selecting the other option, Facebook, opens the standalone Facebook application. You can also use it to share your photos. But since Facebook for HTC Sense and the Facebook application do not share the same login credentials, you'll be asked to sign in again to your Facebook account when you use the Facebook application. The Facebook application only allows you to upload one photo at a time. For more information about what you can do with this application, see Using the Facebook application.