I've released four albums (3 on CD), and it's not an easy task! Especially if you want to sell CDs outside the EU too. You'll run into the bank incompatibility issue (mainly, they take a ridiculous service fee), so you need to arrange something else such as PayPal, although I can't recommend it, due to their... unorthodox methods with the funds. And it's also a lot of work to pack all those CDs and take them to the post office.
Oh and as for using sites to sell your stuff: Amazon, for example, takes 55 % of the original price as a service fee. So if you initially sell a CD for 10 EUR, Amazon still takes 5,5 EUR even if you later on sell the CD for 7 EUR. What I used to use (TheGround, but they stopped CD distribution) took 30 % of the sale price. It's too bad they quit, but I guess it was non-profitable for them.
Right now, I can't sell outside the EU because the bank service fee costs would negate any profit from selling things. Hopefully something else will come along.
But inside the EU (and the rest of Europe), it's fairly simple:
1) User sends you an order, be it by email, order form on a website, or whatever
2) You give the user your SWIFT/IBAN number
3) When the money is in your account, you send the merchandise via your local post office
No extra costs for anyone and it works