when you are in your gallery, there should be an option to "share" it. it then gives you choieces like email, mms, facebook, etc, etc. different phones do it slightly different, but try opening an album and looking for a share icon or menu or settings....or try opening a specific picture and look for this option.
edit: try this:
1.) Press and hold on the picture.
2.) Select Share
3.) Scroll down to "Downloaded Apps"
4.) Choose Facebook.
i apologize for the links, as i copied this from another forum!!!! disregard them.