If you are processing strings, of course you can concatenate them using the + operator:

cString := "Hello" + " " + "from" + " " + "my" + " " + "X#" + " " + "program"

But if you are building longer strings, composed by many substrings, you should use the System.Text.StringBuilder class. Is is much more efficient when dealing with many string parts:

using System.Text

oSB := StringBuilder{}
oSB:Append( "Hello" )
oSB:Append( " " )
oSB:Append( "from" )                                                                                                           
oSB:Append( " " )
oSB:Append( "my" )
oSB:Append( " " )
oSB:Append( "X#" )
oSB:Append( " " )
oSB:Append( "program" )
System.Console.WriteLine( oSB:ToString() )

The StringBuilder class has also a AppendFormat() method, and many other interesting methods to work with the string, like Replace(), Copy() and Insert(). Please see MSDN for more details - specially the System.Text.StringBuilder docs page has a very long and detailled description of this class, together with useful samples.