There are lots of different ways you might have to pay a charge, but luckily most of them can be avoided. If your account has a very high interest rate, there may be a monthly fee attached to it. If you go overdrawn, or a cheque bounces, you can expect to pay a fee of about £30.
If your account comes with a cash card, it should be free to withdraw money at any Link machine, as long as your card is from a bank which participates in the network. If not, or if you withdraw money from a machine belonging to another operator, there will probably be a small charge.