I am a pc Sims player, so I may not be be able to help with specifics to the Xbox.
As far as I understand there are not mods or custom content available for the Sims 4 console players. Here's a post explaining why better than I can.
Why isn't cc allowed in sims 4 console?
https://answers.ea.com/t5/General-Discussion-Feedback/why-isn-t-cc-allowed-in-sims-4-console-I-was-so-looking-forward/m-p/6644283#M3541 If you've never played Sims 4 before on any of the platforms it's on it's hard to explain what a save is, but I'll see if I can try to explain.
You have to launch the game and from the main menu you click the play button. To then save the game you click the options button. It the 3 horizontal dots. Click on that and select Save or it might be Save Game, depending on how the console works.
Exit to main menu to see that you now have a saved game. To load that saved game there should be a Load Game option.
Console players are allowed up to 5 game saves.
It's my understanding the game plays pretty much the same regardless if you're playing on PC, Mac, Xbox or PS4. The only difference is that the consoles don't have access to mods or custom content. And there is no way to transfer the game files from console to PC because they are completely different platforms.
I don't know if this answers your questions fully, if not please head over to EA's AHQ Sims 4 Console Tech Help Board to ask your questions. It may help to get a 2nd opinion.
AHQ's Sims 4 on Console Tech Help Board:
https://answers.ea.com/t5/Technical-Issues-Consoles/bd-p/the-sims-4-technical-issues-consoles-enYou can also look up Youtube videos on how to play the game on Xbox.
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Reference Links:
Little-Known Tips for The Sims 4 on Console
https://www.ea.com/en-gb/games/the-sims/the-sims-4/news/little-known-tipsSims 4 Tips and Tricks - Console Edition
https://www.ea.com/games/the-sims/the-sims-4/console-tips