I know someone who uses half and half to frost there cakes and I was wondering if you need to put sugar in that and how long do you have to whipped it because i tryed to that and it took long time to whipped well lets just it didnt even whipped maybe there a trick to whipped half and half cream, please tell me because i would to try and use it on my cakes

Half and half will not whip on it's own. Only Heavy cream will whip.

Some use half and half in their icing recipes for a bit of richness, instead of water or other liquids.

Another half and half reference can be half shortening and half butter.

Gloria2005, I use 1/2 butter and 1/2 shortening as well as 1/2 & 1/2 in my icings. (both in the same batch) It does turn out a little richer/creamier with the 1/2 & 1/2. I myself can taste the difference. It doesn't take any longer to whip up than normal. give it a try, you might like it.
Donna