Facebook offers a lot of additional features which support being a member of a social network.
Some of them are:
Uploading of pictures and videos, sharing them with friends
Posting of messages on one’s own homepage, comments on them
Using the time line as a display of a chronological sequence of events
Birthday / events calendar
Listening to music
It is up to you what is considered as meaningful for your life. Also new applications certainly will arise.
It is recommended that “grandchildren” explain – as far as they know – these options.