What I always wonder about such questions is:
If someone learns C# how can he/she miss the MSDN site? The .NET docu can be reached by just pressing F1 in VisualStudio on any framework element - and it brings you (context-sensitive) to the documentation:
So have a look at
http://msdn.microsoft.com/en-us/library/system.string.format(v=vs.80).aspx[
^] for string formatting.
before asking further questions of this kind - not that you can't get the answer here (as you see) - I think you will get your answer faster and learn more by reading the documentation. If something there is unclear - that would make a good question...