First you'll need to make a solution of 50g of sodium hydroxide in 150mL of water. Stir it until it completely dissolves. Be careful as it will heat up a lot. Set it aside to cool.
Now get a zinc sheet (we cut one out of a carbon zinc battery in a previous video: http://www.youtube.com/watch?v=knc1lSupAwQ) and attach a wire to it and attach another wire to some steel wool. We then wrap the steel wool with a paper towel to serve as a separator. The zinc is then wrapped around the paper towel/steel wool and the whole assembly is placed into a container. The steel wool has to be exposed to air to allow the oxygen to get in. The electrolyte of sodium hydroxide is added and the battery is ready.