You can use your card abroad just as you would in the UK, it'll work anywhere that accepts Mastercard. There's no extra charges for using your card abroad for payments or cash withdrawals.

You'll always get the Mastercard exchange rate with no fees at the time the funds are taken from your account, just make sure to select the local currency as the currency you'd like to be charged in, as if you select Pounds Sterling, the processor will do their own conversion and the Mastercard exchange rate won't apply.