Since the underlying businesses operate in differing markets, sectors and countries, their quoted prices move independently as supply and demand in them rises and falls and new information is released to the public about the current business situation. It is the changing of prices that offer investors the opportunity to make a capital gain (or loss) via ownership.
This is a more advanced topic for those who want to do what is called « day trading », i.e. those who plan to buy and sell on a daily basis as their main activity. Arbitraging is the process of leveraging price differences between exchanges to make a profit, by buying cryptocurrency cheap on a given exchange and selling it for a higher price on a different exchange.

In contrast, professional fund managers (information here) do not want tips. They have dozens of good ideas of their own. They won't be sharing those ideas with you and they will not be expecting you to share yours. Instead, they ask about how you allocate money. "Which sectors and markets do you like and why?" The difference between these approaches is like night and day.
Dollar-cost average: This sounds complicated, but it’s not. Dollar-cost averaging means investing a set amount of money at regular intervals, such as once per week or month. That set amount buys more shares when the stock price goes down and fewer shares when it rises, but overall, it evens out the average price you pay. Some online brokerage firms let investors set up an automated investing schedule.