want to simplify your question, first you have to find out which exchange has an operational license in your country, so you can use the exchange to sell or buy the bitcoin you want. But this is not talking about the safety of your bitcoins, when you are done buying and not moving to a more secure wallet as suggested on the forums, that's another question you didn't ask and maybe you should look into too.
But you also have to pay attention to this if you don't want your assets to disappear if the exchange encounters a problem. If you're talking about local exchanges that means you should look into it because we can't direct you there if we don't know where you live.
Bitcoin trading is popular due to its decentralized nature, high liquidity, and potential for high returns. There are many options/ways and methods of trading. Proper ways to trade in Bitcoin include choosing a reputable exchange, creating a trading plan, and practicing proper risk management. But prior to adapt the BTC trading, you must learn about the cryptos, about the trending, scaling, technical analysis also. Keep in mind that everything could be easy but not for any one at all. Must take into account about the profit & loss first, than think to invest. After getting satisfactory information and doing solid home work, you will also be able to trade in BTC .