Before the apocalypse, Sanctuary was the home of the main protagonist. You return to this location during the first main quest of the game - Out of time. Later in the game this place becomes the main base of operations of the Minutemen. This place becomes a settlement that you can develop and encourage new settlers to come here.
During your first visit in the settlement, try to check all buildings in search for valuable items. This will provide enough equipment for your next journey.
You can find the Grognak the Barbarian Magazine in your old house. It will add 5% to damage dealt with fists and melee weapons.
You will find Codsworth in the Sanctuary. He will help you in searching through the village. When you meet him the second time, you will be able to invite him to join you.
You will find all workshops that you could need in the village.
In one of the houses you will find a safe on novice level. Watch out, as it is secured with a trap that you must disarm first. Inside you will find some ammunition.