Umm .. well depends on what you want to say to them .. if you want it to be just short and sweet then say something like ..
"Please accept this as my resignation from the company. My last working day will be ....."
Then pad it out with any niceties (if you want to).
Doesnt need to be any more than that .. as long as it states your name, address, the last working day and your signature thats all they need.