"It is a young horse."
Translation:Je to mladý kůň.
It isn't irelevant.
To je kůň. You point to some object and point out that it is a horse.
To je mladý kůň. You comw to a horse and point out that ot is a young horse.
Je to ... is normally used when continuing a conversation. You speak about a horse and during the conversation you say:
Je to mladý kůň.
You say that the horse you are speaking about is a young horse.
In other words, the difference is similar (but not exactly the same) to:
- It's a horse - Je to kůň.
- That's a horse - To je kůň.
Whether it's a question is irrelevant. Questions are marked by a rising intonation in speech and a question mark in writing. If a question contains another verb (other than this "to je/je to" construction), the verb tends to come first in questions.