I'm a newbie, so idk what to invest in, but i wanna build some income on the side.
As a newbie, I would just do what most do and dollar cost average with SPY. By that I mean, invest every month you can and don't look at it for 10-20 years. If you don't want all your investments in the stock market, you can always invest in real estate or a small business. Personally, I've made far more wealth from the RE and Business than stocks.