Most current accounts will come with the option of using an overdraft facility. In some circumstances, as is often the case with student accounts for example, you will be able to enjoy an interest free overdraft, but generally you will have to pay.
The interest charged on your overdrawn balance will be expressed as an APR, or annual percentage rate.
You should be careful to distinguish between authorised and unauthorised overdrafts. An authorised overdraft is one that has been arranged with the bank, and you will pay interest on the overdrawn balance at the agreed rate. When you arrange an overdraft, you will have a limit set upon it. If you exceed this limit, then your overdraft is no longer authorised, and you will find yourself facing hefty charges. Some banks won’t let you spend beyond your limit at all, and so you won’t really have to worry about entering into an unauthorised overdraft but you should always be careful in order to avoid the possibility of racking up large bills.