"¿Cómo estás hoy?"
Translation:How are you today?
Usually "No estoy" when the condition is temporary like how you are feeling.
"No soy" is for more permanent conditions, like gender or name.
Literally, this says "How you-are today?". The verb tells us that the subject is "you" even thouh the "tu" is missing (as is normal in Spanish). So here, as so often, the verb is the big clue as to the meaning.
To translate your version, the verb would need to be "esta" ir "it is".
How would you write..... What is today? I am just trying to differentiate how to write each since the sentence also almost appears to say the same thing. I am a beginner in learning Spanish.
You would use qué instead of cómo, "qué es hoy?". Qué means 'what'.
Duolingo sort of misleads us early learners into thinking cómo means 'what' because of phrases like 'cómo te llamas?' (what is your name), but that phrase actually means something like "how are you called? ... at least in my rough understanding.