Use this command to call a subroutine. Subroutines can be called just writing the name of the already defined subroutine and the arguments. However in situation when the code calls a function that has not yet been defined the interpreter knows that the command is a subroutine call from the keyword CALL.
To be safe you can use the keyword before any subroutine call even if the subroutine is already defined.
Subroutines and functions can be called the same way. ScriptBasic does not make real distinction between subroutines and functions. However it is recommended that functions be used as functions using the return value and code segments not returning any value are implemented and called as subroutine.