Of course you can buy one share at a time. If you want to eventually have a 500 share position, and you buy 1 share at a time, you'll make your broker very happy (and you'll probably go broke )
If you want exposure to an entire stock market or stock market sector, it would be more economical to buy an iShare or similar of the index.
If you keep buying one share of stocks the broker commissions will eat up most of your profits. Consider buying one share of an ETF and using a broker that does not charge commissions on ETF transactions. https://www.valuepenguin.com/best-online-brokerages-commission-free-etfs
i have only 10000 usd no margin so there will be many high priced shares where i will not be able to buy even 100 shares