You apply for a credit card. IF you get it then you have a set limit that they allow you to put on the card. Usually a newbie starts off with $2,000 or $3,000 limit. You charge something, it goes on the card and next month you get the bill in the mail. It'll say the minimum amount they need from you, which is pretty low and generally will take you years to pay off if you follow their schedule, meaning they collect a ton of interest off you.
Rather than drag it out, PAY THE CARD OFF as much as you can each month. You'll have a finance charge added each month you let the majority of the amount ride. If you miss a payment or pay too low (below the minimum) your credit gets dinged. The longer you take to pay off the total, the more you owe since the finance charge adds on each month to the total.
I've put big purchases on my card, but paid it off within 3 months.
Every month you pay it off in full, no interest is put on so you're not paying extra.
Many cards come with a yearly renewal fee, which can be anywhere from $20 to $50 added on once a year. If you order from overseas, you may have an extra fee added to the card as well.
It is NOT free money. It's a loan you get, which you are responsible for paying back.