Microsoft usually has good documentation but on this particular topic I always felt that it was lacking. Here is the MS core documentation for converting a decimal to a string, http://msdn.microsoft.com/en-us/library/59095yyw.aspx.

I recently needed to ensure that I was only getting only two decimal places on a dollar amount as I converted it into a string and was going to write a nice lengthy post myself and then I found this really nice post over at csharp-examples (view post).

Mainly I was looking for the following syntax just to ensure that I was setting up things correctly:

// just two decimal places
String.Format("{0:0.00}", 123.4567);      // "123.46"
String.Format("{0:0.00}", 123.4);         // "123.40"
String.Format("{0:0.00}", 123.0);         // "123.00"

They have some other great custom formatting items as well. Check ‘em out.