5 times? try 13 times... that evening sucked hard for me

Hi, I am new here and already did a lot of reading on the bitcoin. One of the main issues I can't understand is why confirmation takes so long (yes, 2-3 minutes is a LONG time, not to mansion 6 confirmations which can take hours). In today's eCommerce system, when I pay for something, confirmation is instant i.e., I click "confirm" and I am done and can continue about my business.
With bitcoin, how does it work? When I pay to a certain wallet, after how long can I be "sure" the payment arrived? How long will I be hanging in the air until the transaction is complete? What if I choose to make the transaction without a miner's fee? What fee will make the confirmation instant?
If I take it a bit further into the future and want to pay for my groceries in the supermarket, I can't hold the line waiting for a confirmation...