Is it necessary to book before? these days because of the covid19 Or can you just get there and buy tickets there?

You can come and buy there.

You have to reserve the time of the visit at no cost on their page and there you can buy the tickets

I bought my ticket at the same moment

No

You can arrive and buy the tickets there, or you can previously online (you have to select the time and date of arrival).

It is not necessary, you just arrive and buy the ticket. They close at 9pm New York time

It can be reached directly.