Removing the class name before calling a custom function?
public class Class1
{
    public static string UppercaseFirst(string s)
    {
        // Check for empty string.
        if (string.IsNullOrEmpty(s))
        {
            return string.Empty;
        }
        // Return char and concat substring.
        return char.ToUpper(s[0]) + s.Substring(1).ToLower();
    }
}

string MyName = "john";
string result = Class1.UppercaseFirst(MyName)

Result: "John"

public static string UppercaseFirst(this string s)
    {...

public static class StringExtension
{
  public static string UppercaseFirst(this string text)
  {
    // ..
  }
}

string uppercase = "myText".UppercaseFirst();