Fidelity, Ameritrade, Schwab, Robinhood..a bunch don't even charge a fee anymore to trade. Vanguard is the most well know index / ETF funds. An ETF you invest in an entire sector like biotech, industrial, oil etc. instead of one company in that sector if your into that.
Starting early is because you want compound your money..I lost a lot of years staying idle in the market but luckily I've had a 401K with the same company a while for that part of my money.
Compound interest is the phenomenon that allows seemingly small amounts of money to grow into large amounts over time. Compound interest essentially means "interest on the interest" and is the reason many investors are so successful.
www.fool.com
And say you were getting 2% in a money market..which most aren't it takes you 35 years to double your money 0_o
The Rule of 72 determines how long an investment will take to double given a fixed annual rate of interest.
www.investopedia.com