First, collect 16 wood and craft it into a crafting table. Then, find a stretch of dirt and dig till you reach stone using the stair technique. Hollow out a room and place your crafting table and immediately craft 64 sticks.

Craft 2 doors, a wooden pickaxe and a wooden shovel. Shovel some dirt at the surface (Until you get 64) and make a dome around the stairs you made at the surface (Using dirt, you will upgrade later.) and leave a gap for 2 doors.

Place the 2 doors facing outwards in the gaps you made in your dome and keep them shut. Go back into your base and dig another staircase using you pickaxe instead.

After you have reached 5 layers down, hollow out a 10X10 room.
Now you can upgrade. Rebuild your dome with cobblestone, mine for coal and iron and even add multiple rooms.

I hope this guide was helpful.
More blogs will be made soon.