So you open a new bank. I'm the only depositor and I put in $10, say 10 singles.
Next guy comes in to borrow $100. Show me how you make that happen with only 10 singles in the vault. Thanks.
When the other people come up to get a loan, you give them cash/check. You put a marker, a IOU, a ‘loan’ on your books, you then march up to your local Federal Reserve Bank and withdraw the real cash you need, in this example, say 90 dollars. They give it to you, the bank with the ‘loans’ as collateral.
So where does the Federal Reserve get the money? They print it. Sometimes more than the total value of loans and deposit, sometimes less. Usually more.