Getting Started
Sim Settlements requires you "find" the Sim Settlements holotape called "City Manager 2078 Holotape" before you can start using Sim Settlements. Once you find the holotape and load it in your Pip-Boy it will officially activate the Sim Settlements mod and you can start building plots.
If you just play through the Main Quest like normal, you can find the "City Manager 2078 Holotape" and a bunch of ASAM Sensors (required for building plots) in the same place your meet Preston (in Concord - Museum of History) so very lore-friendly.
If you are playing a 2nd (or additional) play through and don't want to go to Concord just yet, the "City Manager 2078 Holotape" can be found in a couple other lore-friendly locations.
Spoiler warning: this page reveals the locations of items that are meant to be discovered during the normal course of game play: Holotape Locations.
You might also want to add 2 other non-Sim Settlement mods that are integrated with Sim Settlements, each of which will enhance your Sim Settlements experience on Xbox: HUDFramework - https://bethesda.net/en/mods/fallout4/mod-detail/335902 Settlement Menu Manager - https://bethesda.net/en/mods/fallout4/mod-detail/4018878
The HUDFramework will give you special "Sim Settlements" HUDmeters that will show up when you are inside a settlement. Settlement Menu Manager will help organize all "Sim Settlements" objects into their own menu inside the workshop tool bar that show up at the bottom of the screen (in workshop mode)