Can I directly buy an index?

Hello there, I'm curious about something regarding indices in the world of finance and investing. Is it possible for an individual investor like myself to directly purchase an index? By that, I mean, can I go to a brokerage account or platform and buy an index the same way I would buy a stock or a mutual fund? I've heard that some indices are represented by ETFs, but I'm not entirely sure if that's the only way or if there are other direct methods as well. Could you clarify this for me, please?