BlackRock is the largest owner of 330 of the S&P500 companies. Similar story for most other markets. So them pushing a somewhat green agenda is actually a big deal and very usefull.
i can't remember the details because i'm poor but they manage other peoples money so a lot of people who care about the environment have money in a 401k or something which means blackrock control the shares they own and vote in shareholder meetings for whatever's best for rich people - there's a way to be more proactive by registering your ownership yourself but i have no idea what it involves.
Kind of. BlackRock operates fonds namely iShares ETFs and also manages investments from other large institutions. That is how they get all those voting rights. Directly registering your shares is necessary so your broker does not exercise your votes. However BlackRock is not a broker, but manages money.