If you've built up a debt on your card it may be worth switching to a card offering a low rate or zero rate, on balance transfers. There are loads of offers out there, read the small print for transfer fees though.
Many companies will allow an extra cardholder on your account as long as the nominated person is over 18 years of age. It is your responsability however, to control that spending, as the contract is in your name.
If you have a 0% card try and pay it off, or switch the balance before the deal ends or you will end up paying interest.
If you shop online regularly it's a good idea to use one of your credit cards solely for this purpose. This way it's easier to check statements for any
anomalies.