See, I always have trouble with 'stock'. I need more details. Is it a stock grant, or an option grant? Because with a publicly traded company, they'll let anyone buy options. The difference is that I don't have to wait 2 years, but I also don't get to wait three years if things aren't great at 2.
It's always stock grants. Only crappy companies give their employees option grants these days. FAANG doesn't do it, as well as the second tier of tech companies (Oracle, Adobe, etc.).
And they will make you rich. Someone who works for these companies at a non-junior level for more than 5-10 years and is reasonable about expenses can quite easily become a millionaire if they work in their offices in developed countries. 5 years for senior positions, 10 years for regular positions.
It’s a grant. You’re given $x value of stock (say $100k). It vests, meaning you can do with what you want, usually at 25% per year, often with a cliff at 1 year and then quarterly/monthly after that.
You may have restrictions on when you can sell depending on your position in the company and other rules.