The ELSE command can only be used between the IF and ENDIF commands. The IF command evaluates to a True or False result, all commands before the ELSE are executed if the result is True. All commands after the ELSE are executed if the result is False.
Example:
$Data = GetUrl("http://gsak.net")
IF Equal(Left($Data,7),"*Error*")
# show the error and cancel the macro
MsgOk msg=$data
Cancel
Else
# Othwise we do something else
# ...
Endif