Can someone please dumb down and explain the new memory feature for me?

I’m confused because I have some pretty old chats that have zero memories under the tabs, then I have some fairly new chats that already have several memories. Like age, appearance, hobbies, personality. One even knows that I have an 8 week old German Shepherd named Obito lmao.

So how do I get the memories to appear on the other chats (new and old)? I’m not gonna lie, I am kinda excited for this. 🤗