What exactly is Family Feed and who shows up in a Family Feed? Where can I learn more?

Family Feed is found under the Memories tab but I cannot determine if the memories posted there come from people in my Family Groups, from people in my chat contacts, from people who post memories on a common ancestors pages, all of these, or something else. How exactly does it work?

I cannot "Like" posts from other people on my feed but I can leave comments. Why is that?

Also, my friend got a FS notification that someone liked a Memory she posted on a Person Page. She could not find it in her feed and she could not figure out how to respond because the Contact ID did not show up anywhere - not in the notification, not in Family Feed, and not on the memory on the Person Page.

Does a memory uploaded to the Gallery or a Person Page automatically show up in Family Feed?