You can use P2P services to buy USDT or bitcoin with your fiat money here you will get many option for payment like mobile Banking, bank Transfer etc. from here you can buy USDT and then exchange with BTC. in this case Binance is most popular exchange so you can follow Binance Exchange.  you  can also use kraken which ultrloa already told about. but my recommend will be always Binance. Because this exchange has a lot p2p users.

Remember that if you intend to buy and hold bitcoins, then after buying bitcoins, withdraw them to a non-custodial wallet or hardware wallet.