For instance, yourText stores your text.

var yourText = "For the second time in three years...";
return yourText.Substring(3,10);

var yourText = "For the second time in three years...";
return yourText.Replace("For","*");

var yourText = "For the second time in three years...";
return yourText.Insert(0, "Hi there.");

var yourText = "email:password";
return Macros.TextProcessing.Split(yourText,":","0").First();

              |
var yourText = "email:password";
return Macros.TextProcessing.Split(yourText,":","all").Count();

var yourText = "email:password:email";
return Macros.TextProcessing.RemoveDuplicates(yourText,":");

var yourText = "email"+System.Environment.NewLine +"password";
return yourText;

var yourText = "{Hi|Hey}";
return Macros.TextProcessing.Spintax(yourText);

var r = new Random();
return r.Next(1,100);

var r = new Random();
return r.NextDouble();

var path = @"D:\file.txt";
return Macros.FileSystem.FileGetLine(path,"2",false);

var path = @"D:\file.txt";
return Macros.FileSystem.FileGetBlock(path,System.Environment.NewLine,"all",false);

var path = @"D:\file.txt";
Macros.FileSystem.FileAppendString(path,"new line", true);

var path = @"D:\file.txt";
return Macros.FileSystem.FileCountOfLines(path);

var path = @"D:\file.txt";
Macros.FileSystem.FileCopy(path,"D:\newfile.txt");

var path = @"D:\";
return Macros.FileSystem.DirectoryCountOfFiles(path);

var path = @"D:\";
return Macros.FileSystem.DirectoryRandomFile(path);

var path = @"D:\";
Macros.FileSystem.DirectoryDeleteFileByMask(path,"*.txt");

var path = @"D:\file.txt";
Macros.FileSystem.DirectoryDeleteFile(path);

var path = @"D:\";
Macros.FileSystem.DirectoryDeleteDirectory(path,true,true);

string regex = project.Variables["myRegEx"].Value;
string text =  project.Variables["textToParse"].Value;
var reg = new System.Text.RegularExpressions.Regex(regex,  System.Text.RegularExpressions.RegexOptions.None);
return reg.Matches(text)[0];

You can operate with ZennoPoster variables in C# code by such a way:

var tmp = project.Variables["variable"].Value;
var counter = System.Convert.ToInt32(tmp);

You can operate with ZennoPoster global variables in C# code by such a way:

var tmp = project.GlobalVariables["[email protected]","globVar"].Value;
var counter = System.Convert.ToInt32(tmp);

Operations with global variables are quite similar to operations with counters.