Why not "if" as in, "If she eats, I drink" e.g. imagine, one partner has a disorder that means they can't eat solid foods, so they drink while partner two eats, when both partners go out together, e.g. to a restaurant?
Wenn sie isst, trinke ich. Correct.
Ich trinke, wenn sie isst. Correct.
Wenn sie isst, ich trinke. Not correct.
The verb of the main clause has to be on position 2. In Duos sentence the subordinate clause is on pos 1. Since the verb has to be on pos 2 it can only be at this place.
so it let me use "if" before but not on this one.I must translate it with "when" though i don't want to.For me when is wann and wenn is if.
"Sie" is only capitalised for the formal "you", not when it means "they" or "her".