Central banks don't print money[1] but investment banks do. Think about it like this: Someone deposits $100. The bank pays interest, to make money on to pay that interest, ~$90 is loaned out to someone.
Now, I still have a bank slip that says $100 in the account, and the bank has given $90 of that to someone else. We now have $190 in the economy! The catch is, that money needs to be paid back, so when people need to call in that cash, suddenly the economy only has $10, because the loan needed to be paid back, causing a cash vacuum.
But that paying back is also where the profit is, because you sell off the loan book, and you can get all your money back, including future interest. So you have lent out $90, sold the right to collect the repayments to someone else as a bond, so you now have $120, a profit of $30
That $30 comes pretty much from nowhere. (there are caveats....)
Now we have my bank account, after say a year with $104 in it, the bank has $26 pure profit AND someone has a bond "worth" $90 which pays $8 a year. but guess what, that bond is also a store of value. So even though its debt, it acts as money/value/whatever.
Now, the numbers are made up, so are the percentages. but the broad thrust is there.
[1] they do