When you are in-game, pause then look at the UI at the bottom middle of your screen. Click on a very small round icon and it opens out allowing you to click on the camera which will take you to your in-game screenshots folder. From there you can scroll through all screenshots you have taken, making them a memory for your sims to reminisce about and getting into the auto-tagged mood and I think it is there you can type a few words at the bottom of the screenshot.
I had trouble with this and it confused me too at first, you can still create emotional memories, EA have just changed how it is done, that's all. As Playalot said, click on the round icon at the bottom of the screen, it will open up three different icons to click on, go into screenshots from there, whatever mood your Sim is in at the time, it will become that kind of emotional memory. For example, if your Sim is Inspired, the screenshot you just captured and selected will become an Inspired memory.
Once done, you have to select another one of those icons to reminisce. Confusing I know but you get the hang of it after a while.
