This is a comment. The compiler ignores comments. Any text between a double-slash and the end of the line constitutes a comment. Here we used the Writeln procedure to send a string to the screen. We did not have a variable declared to read the text from the keyboard.
Lets talk a bit about variables in Delphi.
Delphi is very strict about variables. Variables must be declared so that the compiler can handle them. One of Delphi's greatest assets to me, is the compiler speed. Anyway, a variable is an identifier whose value can change at runtime. Variables are like containers for data, and, because they are typed , they tell the compiler how to interpret the data they hold.