Store cards work in a similar way to credit cards, but you will be restricted to using the card in the chain of stores issuing the card, and you cannot make any cash withdrawals.
The main difference between store cards and credit cards is the rate of interest charged - some of the main store chains have a rate of 30% APR - over double the APR charged on the more competitive credit cards.
This means that if you do have a store card, make sure you pay it off in full every month by direct debit. If you can't do this, use a credit card instead. However, if you are also up to your limit on your credit card, it probably means that you are spending too much for your income anyway - so leave the purchase to a time when you CAN afford it.