If you want to start investing online, just make an account with a brokerage. Vanguard is a good one, I personally use Hargreaves Lansdown, although I don't know if you can make an account if you live outside of the UK with Hargreaves Lansdown. If you are a youngcel, just ask your parents to set one up, I'm sure they would be happy to do so.
If you don't know much about investing, just buy index funds or mutual funds. Plenty of tutorials exist on youtube if you are unsure of how to navigate the site you sign up to. Index funds like the S&P 500 are great, they are essentially a collection of stocks from the top 500 companies in the US, and you are just buying a portion of all of those companies, the funds are run by 'fund managers' who do all the work for you by swapping the companies that do bad with stocks of companies that are doing good. No work on your end, and the S&P 500 has had an average return of 9% per year for the last 62 years. Some years you will get a negative return, don't sell, the market fluctuates and goes up and down, but you will eventually make your money back and then some.
Although I'd hold onto any cash you have for a year or so, strong signs of an economic recession having been brewing in the US for a while now, like the crash of 2008. An economic crash is a great time to buy stocks because they are cheap due to the poor economy, when the markets start to come up again, like they have everytime over the last 100 years, you will make a large return. Even the stock market crash of the 1920's recovered well eventually.
