The gallery is the equivalent to the Sims 3 Exchange. User can upload their creations and others can download them to integrate them in their games.
The gallery can be used from within the game but the community content is only available if you’re actually online. In offline mode you only see your library.
The home tab shows some statistics and a time line which tells you if someone favorites or download your household, if you saved or uploaded and what the people you are following are doing.
I don’t know if you can follow as many people as you want but it seems that the list has nothing to do with your Origin friends list. There are a handful of people I’m now following simply because they were in my Origin friends list automatically but the ones I newly follow are not in my friends list and the other way round.
Messages in your timeline can be deleted by clicking on the cross in the upper right corner (appears if you hover over the message with your mouse pointer or you can check out the household by clicking on the message itself.
The community tab shows every item shared. Only part is loaded at any time though and the rest is loaded once you scroll so that the gallery stays efficient (so far)
You have several options to sort and filter the content. You can filter by people you follow or by stuff that was created by Maxis. Theres also an advanced filter option that lets you filter by size of the household as well as a flag for unowned content which does seem to do much.
You can sort by number of downloads and favorites and this can also be filtered to only show the content of the past 7 days.
Offensive content can be reported by clicking on the flag in the lower left corner.
Next to the filters there’s also a search function where you can search by object name, Origin-ID of the creator or by Hastags. The description of your household can contain hastags (#) so if someone searches for a certain hashtag, Sims with said hashtag in their description will be found.
The gallery makes suggestions once you start typing.
Households marked with a little disc icon are households you have also saved to your hard drive.
Your library shows the Sims which are saved locally on your hard drive. There are also a few created by Maxis which you can’t delete.
You can find them in the following folder on your computer: Documents\ElectronicArts\The Sims 4 Create a Sim-Demo\Tray.
Filtering and search works the same way as on the Community tab but you have additional for my shared content and my Favorites which are missing from the community tab.
Sims with a little cloud in the corner are Sims you have uploaded in the the gallery.
If you click on a household in the gallery or your library, you get a detailed view of the household.
Here you can upload or remove the household to/from the gallery, delete it, edit it in CAS and add a description to your household. Use Hashtags(#) to help other users find your upload.
If you decided you want to edit a household some more you can either replace the household you have in CAS now (not saved changed will be lost) or merge them together. This of course only works if the total of Sims in the two doesn’t exceed 8.
You can also read comments from other users here and check how often a household was downloaded and favorited and you have the option to showcase a household. Showcased household show in the big picture on your profile page (click on your user name)
It’s only possible to showcase your own shared creations.