doubt about sqlserver data types

I'm working with sqlserver express 2005, and I have a lot of doubts about what sqlserver data types use. More exactly my doubt is about text types... nchar, nvarchar, varchar... what are the differences?

thanks.::More exactly my doubt is about text types... nchar, nvarchar, varchar... what are the
::differences?

I really hate to tell you, but there is a documentation for SQL Server that has exact definitions of every data type.