Open a cheap investment account (e.g. Interactive Brokers) and invest in cheap ETFs (e.g. Vanguard Total World Stock and/or Vanguard Total Bond Market - in proportions 70%/30%) until you have 25*your yearly expenses (that usually means 10-12 years of investing, when you save 50% of your salary). After that point, you're FI, you can withdraw (max) 4% a year and live off from returns from your investments ad infinitum.