Either try localbitcoins.com or use a reputable exchange like coinbase or kraken. You can use payment methods like credit card or bank transfer. credit cards are faster but you will get charged higher fees. Bank transfer may take 4-5 days but the fees are minimal!
Coinbase can take weeks to get your account verified. But Kraken does not allow you to buy coins via credit card (as Ciinbase does).
So there are pros and cons to both options...AND these aren't your only options. Bitcoin is a global currency, but start your search based on the country you live in or fiat you'll be using to buy it.