It is not as super sci-fi as people tend to imagine. In fact, it is rather simple.
Dig a tunnel a few feet under ground of a specific length and width. Insert pre-build environments which contain facilities for sleeping, eating, sanitary purposes on one side, leaving the other as a passage.
Have specific protocols to deal with waste. Waste is useful as fertiliser. A green house where vegetable for consumption can be grown is one of the structures in the tunnel. There would also be a sick bay and a command centre.
Seal the entrance with three doors. The first leads into a pause area which would, when closed gain some atmosphere. The second door would open into an area which has atmosphere allowing Outside suits to be removed. The Third door opens into the living area.
The living area would have constantly manufactured air by removing the carbon from exhaled carbon dioxide. The temperature would be set at a constant.
Food would be rationed as would water.
Over time more food would come from the greenhouse, water from waste, so that less needed to be imported.
If the plants grown are properly selected and the quantity carefully monitored, oxygen would be naturally produced.
The prototype could be established on Earth so that translating it to another planet would be simple.