Get a graham craker and break it in half.
On one half put a piece of your favourite chocolate (you can use chocolate chips to make it melt faster).
On top of the chocolate put a big fat white marshmellow ;)
Next get the other half of the graham craker and put it on the top.
Put it in the microwave for about 20-25 seconds. This is my guess though, when the marshmellow has melted it should be done!
(dont worry when the marshmellow expands-like when it poofs out this is okay)