S&P500 index fund

Easiest and lowest cost:

1) Go here : www.keytradebank.be
2) Press the green button on the top right hand of the screen "Become a client" and follow the instructions.
2) Deposit some money.
3) Buy the tracker fund you want. There are lots of them, but the largest, and lowest cost S&P 500 ETF tracker fund has the ticker symbol SPY and it trades on the NYSE. https://www.bloomberg.com/quote/SPY:US

You haven't asked for this, but I will add it: Before you do this, please spend a small amount of money, and some time to understand what you are doing. https://amzn.to/2ScCqkr