In a similar way to how the particle こそ highlights a particular word as being the 'precise' or 'exact' reason for something, its combination with the て-form of a verb will indicate that (B) is absolutely reliant on (A). This reliance can be translated in several different ways, and will usually become clear in the (B) part of sentences. Standard interpretations include 'only if (A), (B)', 'unless (A), (B)', or 'until (A), (B)'.
Only by studying abroad can one appreciate the deliciousness of Japanese food.
It is only when you become a parent that you understand how hard it is to raise a child.
You become a captain only if you take on the responsibility of the whole team.
Only by beating other teams can we become the best in the world.
The reliance that (B) has on (A) can be translated in several different ways, but the most common interpretations are that (A) will determine either the outcome, assessment, or evaluation of (B), based on the speaker's opinion, values, or understanding of the situation.