This achievement is unlocked by story progression in Wintermute mode
You will meet Grey Mother in the town of Milton. her house in the only one lit up. As you are an outsider Grey Mother will not trust you so you have to perform various tasks.
1, She will ask you to fill her firebin(outside her door) with 24hours worth of fuel. this is very simple, go into the abandoned houses and harvest all the wooden furniture. Head down the main path (straight from Mothers house) and you will find the Orca Gas station, this has lots of pallets outside that can be harvested, and should be more than enough. There is also Radio Tower Mast, unmissable look from the town. Right near there is cache with firelogs and near there is a cave with coal.
stick = 8 mins
reclaimed wood = 30 mins
coal = 1 hour
cedar wood = 1 hour
fir wood = 1 hour, 30 mins
2, She requests 8000 calories of food placed in her fridge. Again looting the buildings, particularly the gas station will net you lots of food. listen for crows they are markers for frozen carcesses, harvest deer and wolf meat. When looting buildings check the fridges and cupboards, you will also find lots of tins of food around the floors.
When you have stocked her fridge up, go talk to her, you will advance the story and the achievement will unlock