S&P 500 investing questions

I wanted to buy on Robinhood, but don't see just S&P 500. I'm very new to stocks and investing and know the general idea of the S&P 500. I think I should go with the ETF option. So what would the return yearly be? I think on Robinhood it said 11%? So you get a percent of whatever you invested back. If someone could explain specifically how investing in S&P 500 works that would be awesome. I don't have money to pay a brokerage firm to explain all this.