Step 1: Google what you want to buy
Step 2: Locate a site selling it
Step 3: If that site isn't amazon, buy.com, or another reputable site, check its credentials. If it's an auction site, check that seller's credentials.
Step 4: Check if they ship to your country
Step 5: Click "buy" (or "bid" for auctions)
Step 6: Pay up. Use a credit/debit/gift card, google checkout, or paypal (which all need a credit/debit card. Paypal also lets you use paypal balance if anyone paid you via paypal)
Step 7: Put your address for shipping and wait 1-2 weeks.