Given plenty of fuel, boiling water into steam is easy, the problem is in providing sufficient cooling to condense all the steam into drinking water.

One option is to pass the steam through a coil of pipe in a container of cold seawater.
This water will soon become heated, and should be replaced with cold. The heated salt water should be added to the water in the still, thereby slightly reducing the fuel needed.

There used to be a purpose designed product for distilling seawater, that worked semi automaticly.

Another option would be to use a long length of copper pipe, perhaps fixed to the wall, steam in the top, fresh water out the bottom.
The large area of hot copper pipe could be used for drying food,or laundry.

Please take great care that any improvised boiler or still cant build up any significant pressure, it would explode.
A very simple safety device consists of a vertical pipe open at both ends. The lower end is immersed in the boiling water, the upper end is open to the air.
Any build up of pressure will force the water out of the tube thereby emptying the boiler.
To avoid danger of scalding, the pipe should be angled away from persons.