[Nfqufktc]

At https://www.collinsdictionary.com/di...sh-english/hoy I came across the following example: ¿a qué día estamos hoy? what day is it today?
I would appreciate it if you could explain:

1. Why is it {estamos} and not {es} ?
2. What does {a} in the {a qué} mean compared with the phrase {¿qué día es hoy?}