When your Lite-C script does not include headers, it automatically loads the default.c header. This loads all kinds of definitions and global variables, most of which are defined in the manual.

I suggest you work your way through the strategy tutorial, found here:
https://zorro-project.com/manual/en/tutorial_var.htm

The LookBack global variable is described here:
https://zorro-project.com/manual/en/lookback.htm

The LOOKBACK flag is described here:
https://zorro-project.com/manual/en/mode.htm

The manual is your friend!