How and why is my credit card affected when I open and close a credit card?

How and why is my credit card affected when I open and close a credit card?

Double Negative asked:
I see a great deal at a store to open up a credit card and get a prize or a rebate. If I want the big discount I open the credit card and then get the discount but I don’t want or need the credit card at all.
Is it better to