If you want to accept credit cards for your business, you will need to get a merchant account. Basically, this is a contract between you and the bank in order for you to be given a line of credit. Without it, your customers will have to pay you through other means.
The merchant account is more important when you open an online business. This is because customers can only see your products using their web browser and if they want to order, this is the one of the means of paying for it.
The problem with having a merchant account online is the fact that it is very expensive when you are just starting out which also includes filling up various forms and a background check.
To skip this, a lot of entrepreneurs decide to get a third party payment processor to accept credit card payments. A good example of this is Paypal which charges a certain percentage for every sale made.
Another provider is 2checkout.com. The difference with them is that they charge you a $49 set up fee and their rate is $.45 cents plus 5.5% per transaction.
You may also consider WorldPay which is useful for entrepreneurs operating outside the US. The downside is that you have to pay a monthly fee of about $50 per month and pay a one time set up fee of $400. The transaction fees are also higher because their rate is $.40 cents plus 3.25% per transaction.
There are a few third party processors that are able to process your payments digitally.
You have clickbank that charges you a dollar plus 7.5% per transaction. You have to pay a one time registration fee of about $49.95. Being a member, one of the perks is earning commission from them when you decide to use of their affiliate programs to sell your products.