Ask HN: What are your instruments for investment?

I am going to get my first salary so I was looking around for investment options. Do you have any advice for someone just starting out? How do you manage your investments? Any apps/services that stand out? Also, any resources for understanding index funds would be great. I know they are a basket of securities but I don't understand why they're traded on the stock market just like a stock. Because if they're traded on the stock market then they're prone to be affected by the forces that affect the stocks.