Replicating winning strategies
Most people know about Warren buffet, one of the richest people on the planet who reached this status all by choosing the right stocks. People like Warren Buffet analise stocks and make calculated investment decisions, he, like most other hedge fund managers, also receive info before normal people. Warren Buffet has a winning strategy that he has developed over time.
The hard work has been done for you
People like warren buffet comb through mounds of info before they make an investment decision, this uses a lot of time, time which we sometimes don't have. Luckily on todays era we have access to the portfolios of major investors, investors like Warren Buffet need to file reports to the SEC(Securities and Exchange Commission) in order to maintain transparency on their investment and prevent insider trading.
These reports show what stocks they are investing in and what the allocation is of these stocks in their portfolios. Once you have all these info you can construct your portfolio accordingly and also reap similar benefits.
Besides coppying well know investors you can also look at the compositions of ETFs(Exchange traded funds) in order to see what they are investing in and what their allocation is. To see the underlying stocks in ETFs you can go onto the company that manages the fund, and download the fact sheet from their website, most countries require ETFs to indicate what stocks they invest in(usually their top 10 by allocation).