It's not just Barclays, they are just the rirst to be fined.
OK
Barcalys part A is the one you see on the high st
Barclays part B is the one that deals with buying and selling shares / bonds / making big money for the bankers bonuses.
Barclays part A lends to people like you and me, but they don't actually have any money, they borrow it from Barclays part B. T
So Part A borrows the money and pays interest on the loan, then they lend the money to us and charge interest. The difference between the interest they pay and the interest they charge us profit.
Part A and Part B are not suposed to communicate, Part B is supposed to lend to any bank that wants to at the going rate.
Their profit is the interest part A pays to part B.
What they have been fined for is A and B talking to each other, then Part B charges more interest on loans to B, thus increasing the profit of B.
Part A then lends the money to us at a higher rate and makes a profit.
The bankers get a bonus based on the profit.