It's actually very easy. Most airlines don't even issue paper tickets anymore, so the odds of having one are very small.
Paper tickets, when they even exist, are mailed to you, picked up at the airport, or bought from a travel agent. There is a separate coupon for every flight plus a receipt coupon. Airlines charge extra for them, so you would have paid an extra fee. If you bought it online, the website would also have charged you a mailing fee.
If you were sent an e-mail receipt and nothing else, and you didn't pay any extra charges for a paper ticket or mailing fees, then you have an e-ticket.