Its not that simple, and as you discovered the help file is not complete yet. Please read the tutorial thread first, or look at the example scripts on my FontCreator Review page.
First you need to define the feature, then the lookup tables, then the substitutions. The syntax must be correct too:
script latn {
feature Ligatures;
}
feature Ligatures liga {
lookup ligaSub;
} lookup ligaSub {
sub t e s t → zero;
}
Even then, I am not sure uniF001 will be exported, so try with
sub t e s t → zero;
That compiles correctly.