Train stations in Japan have many platforms and it can be quite confusing to find the correct platform to go to for your train. Boarding a train at the wrong platform can be a hassling experience.
You can ask “~ hoomen wa nanbansen desuka”. Hoomen means “in the direction of” and nanbansen means “what platform number”. The reply you are expecting is “(number) bansen”, for example, “ichi bansen” (platform one).
Just listen out for the number and you’d be good to go.