You need to buy and transfer from exchanges as mentioned.
List of exchanges where you can buy --> https://cryptocoincharts.info/markets/info
Correction you must convert your money or buy bitcoins before you transfer it to your bitcoin core wallet because if you directly send the money to bitcoin core wallet it wouldn't work. So you must convert your money or buy bitcoin to be able to transfer the bitcoin to your bitcoin core wallet.List of exchanges where you can buy --> https://cryptocoincharts.info/markets/info
You can buy bitcoins from Coinbase or Localbitcoins this exchanges that I think trusted but in Localbitcoins you must trade to trusted traders only don't deal to newbies and no trading history.
As we are in the bitcoin forum, I usually take it if someone asks about money = bitcoin and he's asking to transfer it to a bitcoin wallet so I think that's understandable.
@OP USD/fiat/money --> exchange --> bitcoin --> bitcoin core wallet
