How does RSU stock vesting works ?

I got a few RSUs couple of years back when I joined a tech firm and starting June 2022, My stocks will vest (kind of unlock in phases till 2025).

I wanted to know few things ?

1) Is it required to sell the stock immediately in June itself or I can sell anytime ? I would not prefer to sell right now because the price just keeps going down

2) How are thesw RSUs taxed ?